This paper describes the diet and foraging behaviour of Adelie penguins (Pygoscelis adeliae) at  Béchervaise Island during 1998/99, a season of low breeding success. Fifty-six percent of nests with eggs failed during the three weeks following first hatch. A breeding success of 0.43 chicks cr6ched per nest was achieved, compared to previous seasons with higher annual breeding success rates ranging from 0.69 to 1.06 chicks créched per nest. Evidence from analyses of foraging location, foraging trip duration and diet suggests that the death of chicks during the guard stage was due to an inadequate rate of food supply. In most previous seasons adults have foraged both at the continental shelf edge (particularly females) and locally (particularly males). This season male penguins carried out fewer local trips and both sexes spent longer at sea than in years of higher breeding success. Meal masses brought back to the chicks were within the normal range but extended foraging trip durations reduced feeding frequency. These findings contrast with observations made in 1994/95 (a season in which all chicks died of starvation), when smaller meals were delivered and birds foraged further offshore than in this or any other season studied. The significance to CCAMLR of these variations in foraging behaviour is discussed.