The effects of sex, ontogeny, and season on the diet of Ranitomeya virolinensis were studied over one year. The diet of this Andean species is composed mainly of small prey; the most important prey categories according to index of relative importance (IRI) were Acari, Formicidae, Holometabolous larvae, and Collembola. There were no differences in total prey gut content over time assessed in number and volume; however, the diet composition of this Santander Poison Frog changed between dry and wet seasons, with Formicidae, holometabolous larvae and Collembola as the prey categories that contributed most to the difference. Males had fewer prey in their guts than females, but there were no compositional differences between sexes. There was a shift in the importance of prey caused by ontogeny. Mean prey volume increased with body size, whereas the occurrence of Acari and Formicidae varied inversely with SVL. Formicidae was the second most important prey category according to IRI. Therefore it is an important category as has been described previously for other Dendrobatid species. However, its importance fluctuated with the season. Acari was the most significant prey type in R. virolinensis as is the case for other small related species of the genus, although its importance changed with the ontogeny. The diet of this frog had a substantial phylogenetic component because closely related species have similar diets; nevertheless, its diet is clearly affected by other intrinsic and extrinsic factors.