A study of Dall’s porpoise distribution and behaviour between September 1986 and February 1989 confirmed the year-round presence of these animals in Monterey Bay, California. Dall’s porpoises in the Bay preferred deep (mean = 264 m) waters near the head of the Monterey Submarine Canyon. Mean group size was5.7, but aggregations of up to 20 animals periodically developed. Most porpoises sighted in the Bay were subadults, and cow-calf pairs were uncommonly seen. Bow-riding was common, occurring in over half of the sightings, and rooster-tailing was the predominant surfacing mode. Monterey Bay Dall’s porpoises spent most of the day feeding, resting, and playing in scattered subgroups of 2-6 individuals.