The comparative diet and body size of the Four-Lined Snake (Elaphe quatuorlineata), one of the largest and more vulnerable species of snakes in Mediterranean central Italy, were studied in five different habitats. Data given here collated both literature and original data. Overall, females were significantly larger than males but the strength of these differences varied considerably with sample size. Overall, small mammals (almost exclusively rodents) accounted for the main part of the diet (66.7%), followed by birds and their eggs (mainly Passeriformes; 26.4%), and by lizards (6.9%), although the number of eggs in the diet was probably greatly underestimated. In qualitative terms, both sexes fed on the same prey types, but, quantitatively, males and females differed significantly in terms of prey composition; females fed on more birds and fewer lizards than males. Rodents were the most important prey source in most habitat types, although birds were preyed upon slightly more frequently in the wet habitat than rodents, which, nonetheless, still represented a important prey source. Four-Lined Snakes started feeding in early April and continued feeding until early November. The monthly frequency of occurrence of birds in snake stomachs differed significantly from that of small mammals; birds were taken almost exclusively in April and May (and mainly by females), and small mammals were taken all throughout the annual feeding cycle of snakes.