The European hake, Merluccius merluccius, is an important resource for Mediterranean fisheries. This study focuses on juvenile and adult hake feeding ecology in the Gulf of Lions, using information from scientific surveys carried out during two seasons and three years (2004-2006). Stomach content and stable isotope (δ15N, δ13C) analyses were performed, and the main factors explaining variations in δ15N were investigated using GLMs. In the Gulf of Lions, hake mostly fed on crustaceans and fish and a dominant piscivorous regime was reached at 15 cm total length. Pelagic fish (sardine, anchovy and small blue whiting) were the main source of prey (40%-80%) and cannibalism was low (<5%). The results confirmed that hake is an opportunistic feeder and also showed that the size and diversity of prey vary among hake size classes, probably as a result of the different spatial distribution and/or foraging migrations. The present study finally postulates that the unbalanced sex ratio (80% female against 20% male) observed at the adult stage could be related to the combination of growth pattern differences, diet and exploitation rate on the continental shelf, where the males spend a longer period of time.