Several important aspects of reproduction in the female sea otter, such as gestation, pupping frequency, period of pup dependency, and annual pupping rate, were unclear when this study was begun. We present data from 75 tagged adult females that indicate gestation is variable, but on average is about 6 months, the length of pup dependency is 6 mo, thus the pupping interval is usually 12–13 mo. Most females breed for the first time in their fifth year of life. About 85–90% of adult females pup in a given year.