Studying the diet of top marine predators, such as seabirds, is important in understanding their place in the trophic network and effects of global climate change, but knowledge of the diet of several procellariiformes remains anecdotal. The diet of Bulwer's Petrel (Bulweria bulwerii) in the Azores was studied over two consecutive years using stomach flushings from 85 birds. The frequency of occurrence of prey taxa (%0) was similar in both years (χ2 = 5.396, d.f. = 5, p = 0.370), with squid being the most common. Fish and squid were of similar occurrence by number (%N) in the diet (49% and 51%, respectively) in 1998 but in 1999 fish were more numerous (62% against 38% for squid). Squid lower beaks from five families and fish otoliths from six families were identified, representing 20 taxa. The most abundant prey in both years were squid Pyroteuthis margaritifera and the mesopelagic fish Electrona risso. The maximum standard length offish and squid consumed was 7 cm and 11 cm, respectively. Given most of the identified prey are luminescent, the findings corroborate earlier studies suggesting Bulwer's Petrel feed on small mesopelagic prey that migrate to the surface at night.