Leprosy affects skin and peripheral nerves, and acute inflammatory type 1 reactions (reversal reaction) can cause neurologic impairment and disabilities. Single skin lesion paucibacillary leprosy volunteers (N = 135) recruited in three Brazilian endemic regions, treated with single-dose rifampin, ofloxacin, and minocycline (ROM), were monitored for 3 years. Poor outcome was defined as type 1 reactions with or without neuritis. IgM anti-phenolic glycolipid I, histopathology, Mitsuda test, and Mycobacterium leprae DNA polymerase chain reaction (ML-PCR) were performed at baseline. chi(2) test, Kaplan-Meir curves, and Cox proportional hazards were applied. The majority of volunteers were adults with a mean age of 30.5 +/- 15.4 years; 44.4% were ML-PCR positive. During follow-up, 14.8% of the patients had a poor clinical outcome, classified as a type 1 reaction. Older age (> or = 40 years), ML-PCR positivity, and lesion size > 5 cm were associated with increased risk. In multivariate analysis, age (> or = 40 years) and ML-PCR positivity remained baseline predictors of type 1 reaction among monolesion leprosy patients.