Background Wild golden lion tamarins from the Biological Reserve of Poc¸o das Antas, Rio de Janeiro, Brazil, have high prevalence of Trypanosoma cruzi infection leading us to clinically assess the disease in this endangered species. Methods 34 tamarins were sampled for the presence of T. cruzi infection (through serology) and clinical evaluation (electrocardiography, blood counts and biochemical analysis). Results 32% of the sampled tamarins were T. cruzi positive, 45% of these displayed cardiac abnormalities. Main cardiac abnormality in infected tamarins was T wave low voltage; R wave low voltage and V3S wave high voltage were also found. The tamarins displaying T wave low voltage had high proportion of seric cardiac creatine kinase. Seric mean total protein was significantly higher in infected tamarins. Conclusions Sampled tamarins displayed typical signs of T. cruzi infection, similar to experimentally infected primates and human natural infection. Potential risk of T. cruzi infection to this endangered species is discussed.