INTRODUCTION: While many believe that older adults fall more often during the winter months, research on this is inconclusive. This study used nationally representative data from 2001 to 2002 to examine unintentional fatal fall rates among older men and women by season and climate, and nonfatal fall rates by season. METHODS: We studied fatal and nonfatal unintentional falls among U.S. adults aged > or =65 during December 2001-November 2002 by season. Fatal fall data were obtained from National Center for Health Statistics' annual mortality tapes; nonfatal fall data for injuries treated in emergency departments were obtained from the National Electronic Injury Surveillance System All Injury Program. Fatal falls were also analyzed by climate based on each state's average January 1, 2001 temperature (colder climates < or =32 degrees F (0 degrees C) and warmer climates >32 degrees F (0 degrees C)). RESULTS: From December 2001 through November 2002, neither fatal nor nonfatal fall injury rates showed any seasonal patterns. For fatal falls, the average rate was 9.1 percent higher in colder climates, regardless of season. CONCLUSION: Among older adults, fatal fall rates appear to be influenced more by climate than by season. Additional research is needed to clarify the mechanisms underlying these observations.