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Between 1978 and 1985, denning ecology of the black bear (Ursus americanus) was studied in the Kenai Peninsula, the Susitna River basin, and Prince William Sound, Alaska. All these populations are near the northern extension of their range. In different years the mean number of days spent in dens varied from 189 to 233 days; the maximum time spent in a den by an individual bear was 247 days. Timing of emergence in the spring and entrance in the fall appeared most related to time of year and secondly to weather, snow accumulation and melt, and food availability. Bears in the more severe climate along the Susitna River entered dens almost 2 weeks earlier and emerged later than bears on the warmer Kenai Peninsula. Chronology of denning differed among pregnant females and other sex and age groups, but overlap occurred with all age and sex groups. Site selection, vegetation type, and den type (cave, tree, excavated) varied with area and was related to winter weather conditions (rain vs. snow), soil type (deep vs. shallow and rocky), and topography of the areas (mountains vs. flats). Den morphometry was compared among areas. Denning chronology was compared with that of other North American black bear populations and with current denning theory.