Knowledge of foraging ecology of endangered mammals is often based on limited data because of logistical constraints of accessing animals, their stomach contents, or fecal samples. Here we use a stable isotope approach to examine feeding habits of a rare mammal, gaining insights over a greater temporal scale than a traditional fecal analysis would allow, and ameliorating some of the constraints of reduced sample sizes that can limit studies of mammalian foraging ecology. We focus on the endangered pygmy raccoon (Procyon pygmaeus), an endemic species from Cozumel Island, Mexico. Raccoons are thought to be omnivorous based on studies in the temperate zone, yet few dietary analyses have been conducted on raccoons in the tropics. Using hair and blood samples obtained from trapping over 3 years (2001–2003) and at 3 localities, the feeding habits of this species were examined based on the isotopic ratios of nitrogen (δ¹⁵N) and carbon (δ¹³C). Feces also were collected to supplement and compare to isotopic data. Both isotopic data and scat analyses suggest an omnivorous diet specialized on crabs, which constituted >50% of the diet, followed by fruits and insects. Hair and blood samples did not significantly differ in carbon or nitrogen isotopic ratios and we found no age- or sex-related variation. Although we observed subtle spatial and temporal variation in diet, both stable isotope and fecal analyses emphasize the dominance of crabs across these scales.