diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -2113,6 +2113,8 @@
     'PhabricatorCalendarImportEditor' => 'applications/calendar/editor/PhabricatorCalendarImportEditor.php',
     'PhabricatorCalendarImportEmptyLogType' => 'applications/calendar/importlog/PhabricatorCalendarImportEmptyLogType.php',
     'PhabricatorCalendarImportEngine' => 'applications/calendar/import/PhabricatorCalendarImportEngine.php',
+    'PhabricatorCalendarImportEpochLogType' => 'applications/calendar/importlog/PhabricatorCalendarImportEpochLogType.php',
+    'PhabricatorCalendarImportFrequencyLogType' => 'applications/calendar/importlog/PhabricatorCalendarImportFrequencyLogType.php',
     'PhabricatorCalendarImportICSFileTransaction' => 'applications/calendar/xaction/PhabricatorCalendarImportICSFileTransaction.php',
     'PhabricatorCalendarImportIgnoredNodeLogType' => 'applications/calendar/importlog/PhabricatorCalendarImportIgnoredNodeLogType.php',
     'PhabricatorCalendarImportListController' => 'applications/calendar/controller/PhabricatorCalendarImportListController.php',
@@ -6940,6 +6942,8 @@
     'PhabricatorCalendarImportEditor' => 'PhabricatorApplicationTransactionEditor',
     'PhabricatorCalendarImportEmptyLogType' => 'PhabricatorCalendarImportLogType',
     'PhabricatorCalendarImportEngine' => 'Phobject',
+    'PhabricatorCalendarImportEpochLogType' => 'PhabricatorCalendarImportLogType',
+    'PhabricatorCalendarImportFrequencyLogType' => 'PhabricatorCalendarImportLogType',
     'PhabricatorCalendarImportICSFileTransaction' => 'PhabricatorCalendarImportTransactionType',
     'PhabricatorCalendarImportIgnoredNodeLogType' => 'PhabricatorCalendarImportLogType',
     'PhabricatorCalendarImportListController' => 'PhabricatorCalendarController',
diff --git a/src/applications/calendar/import/PhabricatorCalendarImportEngine.php b/src/applications/calendar/import/PhabricatorCalendarImportEngine.php
--- a/src/applications/calendar/import/PhabricatorCalendarImportEngine.php
+++ b/src/applications/calendar/import/PhabricatorCalendarImportEngine.php
@@ -63,6 +63,67 @@
       }
     }
 
+    // Reject events which have dates outside of the range of a signed
+    // 32-bit integer. We'll need to accommodate a wider range of events
+    // eventually, but have about 20 years until it's an issue and we'll
+    // all be dead by then.
+    foreach ($nodes as $key => $node) {
+      $dates = array();
+      $dates[] = $node->getStartDateTime();
+      $dates[] = $node->getEndDateTime();
+      $dates[] = $node->getCreatedDateTime();
+      $dates[] = $node->getModifiedDateTime();
+      $rrule = $node->getRecurrenceRule();
+      if ($rrule) {
+        $dates[] = $rrule->getUntil();
+      }
+
+      $bad_date = false;
+      foreach ($dates as $date) {
+        if ($date === null) {
+          continue;
+        }
+
+        $year = $date->getYear();
+        if ($year < 1970 || $year > 2037) {
+          $bad_date = true;
+          break;
+        }
+      }
+
+      if ($bad_date) {
+        $import->newLogMessage(
+          PhabricatorCalendarImportEpochLogType::LOGTYPE,
+          array());
+        unset($nodes[$key]);
+      }
+    }
+
+    // Reject events which occur too frequently. Users do not normally define
+    // these events and the UI and application make many assumptions which are
+    // incompatible with events recurring once per second.
+    foreach ($nodes as $key => $node) {
+      $rrule = $node->getRecurrenceRule();
+      if (!$rrule) {
+        // This is not a recurring event, so we don't need to check the
+        // frequency.
+        continue;
+      }
+      $scale = $rrule->getFrequencyScale();
+      if ($scale >= PhutilCalendarRecurrenceRule::SCALE_DAILY) {
+        // This is a daily, weekly, monthly, or yearly event. These are
+        // supported.
+      } else {
+        // This is an hourly, minutely, or secondly event.
+        $import->newLogMessage(
+          PhabricatorCalendarImportFrequencyLogType::LOGTYPE,
+          array(
+            'frequency' => $rrule->getFrequency(),
+          ));
+        unset($nodes[$key]);
+      }
+    }
+
     $node_map = array();
     foreach ($nodes as $node) {
       $full_uid = $this->getFullNodeUID($node);
diff --git a/src/applications/calendar/importlog/PhabricatorCalendarImportEpochLogType.php b/src/applications/calendar/importlog/PhabricatorCalendarImportEpochLogType.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/importlog/PhabricatorCalendarImportEpochLogType.php
@@ -0,0 +1,34 @@
+<?php
+
+final class PhabricatorCalendarImportEpochLogType
+  extends PhabricatorCalendarImportLogType {
+
+  const LOGTYPE = 'epoch';
+
+  public function getDisplayType(
+    PhabricatorUser $viewer,
+    PhabricatorCalendarImportLog $log) {
+    return pht('Out of Range');
+  }
+
+  public function getDisplayDescription(
+    PhabricatorUser $viewer,
+    PhabricatorCalendarImportLog $log) {
+    return pht(
+      'Ignored an event with an out-of-range date. Only dates between '.
+      '1970 and 2037 are supported.');
+  }
+
+  public function getDisplayIcon(
+    PhabricatorUser $viewer,
+    PhabricatorCalendarImportLog $log) {
+    return 'fa-clock-o';
+  }
+
+  public function getDisplayColor(
+    PhabricatorUser $viewer,
+    PhabricatorCalendarImportLog $log) {
+    return 'red';
+  }
+
+}
diff --git a/src/applications/calendar/importlog/PhabricatorCalendarImportFrequencyLogType.php b/src/applications/calendar/importlog/PhabricatorCalendarImportFrequencyLogType.php
new file mode 100644
--- /dev/null
+++ b/src/applications/calendar/importlog/PhabricatorCalendarImportFrequencyLogType.php
@@ -0,0 +1,38 @@
+<?php
+
+final class PhabricatorCalendarImportFrequencyLogType
+  extends PhabricatorCalendarImportLogType {
+
+  const LOGTYPE = 'frequency';
+
+  public function getDisplayType(
+    PhabricatorUser $viewer,
+    PhabricatorCalendarImportLog $log) {
+    return pht('Too Frequent');
+  }
+
+  public function getDisplayDescription(
+    PhabricatorUser $viewer,
+    PhabricatorCalendarImportLog $log) {
+
+    $frequency = $log->getParameter('frequency');
+
+    return pht(
+      'Ignored an event with an unsupported frequency rule ("%s"). Events '.
+      'which repeat more frequently than daily are not supported.',
+      $frequency);
+  }
+
+  public function getDisplayIcon(
+    PhabricatorUser $viewer,
+    PhabricatorCalendarImportLog $log) {
+    return 'fa-clock-o';
+  }
+
+  public function getDisplayColor(
+    PhabricatorUser $viewer,
+    PhabricatorCalendarImportLog $log) {
+    return 'red';
+  }
+
+}