Analyses of dental variation in geographically restricted, wild populations of primates are extremely rare; however, such data form the best source for models of likely degrees of variation within and between fossil species. Data from dental casts of a geographically restricted population of moustached tamarins (Saguinus mystax mystax) from Padre Isla, Peru, document high levels of dental variability, as measured by coefficients of variation, in a nonsexually dimorphic species, despite its isolation and small population size. Like other primates, moustached tamarins show lower variability in the dimensions of the first molars and increased variability in the dimensions of the final molars in the toothrow. Moustached tamarins from Padre Isla have a distinctive pattern of variability in the remaining teeth, including more stable tooth lengths in the anterior and posterior portions of the toothrow, and more stable tooth widths in the midregion of the toothrow. High variability in incisor width may be due to age effects of a distinctive diet and pattern of dental wear.