The common sole Solea solea Linnaeus, 1758 was collected from the Ebro Estuary each month (January-December) throughout 1987. The compostion of its natural diet was examined, and the possible influence of sex and age on prey selection. The contents of 461 stomachs were analyzed by means of frequency of occurrence, numerical abundance and Simpson's prey-dominance index in order to determine the dominant, occasional or accidental prey categories; 43 different families of prey were classified. Crustaceans comprised 54.9%, polychaetes 34.1% and molluscs (10.9%) of its diet. Significant differences in the basic diet were observed as a function of sex and age. Examination of the contents of the alimentary tracts revealed that males and females have different diets even when sharing the same habitat. The age-class groups also have different diets, smaller prey being replaced by increasingly larger food items with increasing age (size). © 1991 Springer-Verlag.