Helminth identification and egg counts were performed in 316 fecal samples during 4 years in 199 golden lion tamarins (GLTs), Leontopithecus rosalia, from two Brazilian conservation units. Tamarin sex and age, area of occurrence and helminth co-infection were tested as potential factors that could affect helminth prevalence and egg shedding in host individuals. Three nematodes species were found at low prevalences but not in both conservation units: Ancylostomatidae (12%), Ascarididae (1%) and Tripanoxyuris minutus, an Oxyuridae (4%). Three other species had high prevalences and were found in both conservation units: one acanthocephalan, Oncicola sp. (30%), and two nematodes, Spiruridae (24%), and Trichostrongylidae (31%). These three latter helminths had distinct prevalences between the conservation units, probably due to differences in availability of helminth infective stages in each area. Prevalences were greater in females for all helminth species; this was especially the case for Oncicola sp. Sex and age differences in helminth prevalence may be associated with changes in sexual steroid levels that accompany age and reproductive status. Frequency of simultaneous infections by the two helminths considered most pathogenic (Oncicola and Trichostrongylidae) were statistically lower than expected; this may be related to: (i) higher tamarin death rate caused by the association; (ii) differences in exposure to helminth infective stages in the various areas of occurrence; (iii) and competition between these helminth species. All helminth species followed a negative binomial distribution, with stronger clumping occurring in Trichostrongylidae and in female GLTs. Distinct transmission strategies of Oncicola sp. and Spiruridae, in contrast with Trichostrongylidae, may partially explain the different clumping levels of these helminths in GLTs. Mean fecal egg counts of all helminths were not different between GLT sexes, ages or areas of occurrence. The three most common helminth species may be a threat to isolated or dense GLT populations.