Little is known about the fatty acid composition of foods eaten by wild primates. A total of 18 staple foods that comprise 97% of the annual dietary intake of the mountain gorilla (Gorilla beringei) were analyzed for fatty acid concentrations. Fruits and herbaceous leaves comprise the majority of the diet, with fruits generally having a higher mean percentage of fat (of dry matter; DM), as measured by ether extract (EE), than herbaceous leaves (13.0% ± SD 13.0% vs. 2.3 ± SD 0.8%). The mean daily EE intake by gorillas was 3.1% (DM). Fat provided ≈14% of the total dietary energy intake, and ≈22% of the dietary non-protein energy intake. Saturated fatty acids accounted for 32.4% of the total fatty acids in the diet, while monounsaturated fatty acids accounted for 12.5% and polyunsaturated fatty acids (PUFA) accounted for 54.6%. Both of the two essential PUFA, linoleic acid (LA, n-6) and α-linolenic acid (ALA, n-3), were found in all of the 17 staple foods containing crude fat and were among the three most predominant fatty acids in the diet: LA (C18:2n-6) (30.3%), palmitic acid (C16:0) (23.9%), and ALA (C18:3n-3) (21.2%). Herbaceous leaves had higher concentrations of ALA, while fruit was higher in LA. Fruits provided high amounts of fatty acids, especially LA, in proportion to their intake due to the higher fat concentrations; despite being low in fat, herbaceous leaves provided sufficient ALA due to the high intake of these foods. As expected, we found that wild mountain gorillas consume a diet lower in EE, than modern humans. The ratio of LA:ALA was 1.44, closer to agricultural paleolithic diets than to modern human diets. Am. J. Primatol. © 2013 Wiley Periodicals, Inc.