Data from a six-year follow-up of Trypanosoma cruzi-infected adolescents enrolled in a randomized, double-blind, clinical trial of benznidazole showed successful chemotherapy in 64.7% (95% confidence interval [CI] = 50.2-78.7) and 84.7% (95% CI = 66.8-92.9), respectively, by intention-to treat and by per protocol analysis measured by seronegativity in a chemiluminescent enzyme-linked immunosorbent assay with a purified trypomastigote mucin antigen. No incident case of cardiomyopathy was detected by electrocardiogram assessment in this cohort of adolescents who had been infected in childhood. The persistent and consistently long-term negative serologic reactions suggest the absence of the parasite in the treated patients and reinforces the recommendation of early benznidazole chemotherapy for T. cruzi-infected infants as a public health policy in endemic areas.