This study describes the stomach contents of 95 harbor porpoises (Phocoena phocoena) killed in groundfish gill nets in the Gulf of Maine between September and December, 1989-94. The importance of prey was assessed by frequency of occurrence, numerical proportion, and proportion of ingested mass. Atlantic herring (Clupea harengus) was the most important prey, occurring in 78% of noncalf porpoise stomachs and contributing 44% of ingested mass. Pearlsides (Maurolicus weitzmani), silver hake (Merluccius bilinearis), and red and white hake (Urophycis spp.) were common prey items. There were no significant differences among diets of sex and maturity groups. but the calf diet differed significantly from adults in number of Atlantic herring eaten and the total mass of food consumed. At four to seven months of age, calves were eating pearlsides, small silver hake, and euphausiids (Meganyctiphanes norvegica) while still nursing.