Despite relatively mild weather, black bears (Ursus americanus) entered dens and remained for an average of 126 days. Bears entered their dens during a 5-wk period that began on Oct. 21st. A significant difference (P < 0.05) was found among the average dates of den entrance of adult females, yearlings and adult males. Adult females were the 1st bears to enter their dens; yearlings entered next, and adult males entered last. The stimulus to enter a den probably was provided by the cumulative effect of weather. The actual period of winter dormancy was preceded and followed by periods of increased inactivity. Inactivity during the predenning and postdenning periods was correlated with daily weather, principally maximum daily temperature and precipitation.