Objectives: To assess the safety of benznidazole use in adult patients with chronic Chagas’ disease. Methods: The Naranjo algorithm was applied to classify the causality of adverse drug reactions (ADRs). Results: In total, 190 patients were treated with benznidazole over a period of 4–180 days (mean 58.90+36.54 days) with a dose of 50–500 mg/day (221.33+57.16 mg/day). Of the 190 patients treated, 93 had ADRs and 59 of these interrupted treatment. There was a higher incidence of ADRs among female and young adult patients. There was a higher incidence of ADRs during the first 30 days of treatment. Interruption of treatment was more frequent in women. Among the patients who interrupted treatment, 39 had mild ADRs, 19 had moderate ADRs and 1 had a severe ADR. There were no interruptions in treatment for 97 patients without ADRs. The survival curves indicated that the time until interruption of treatment in patients with moderate and severe ADRs was lower than in patients with mild or no ADRs. The most frequent disorders were in the skin (26.3%), gastrointestinal system (9.5%) and nervous system (5.3%). Conclusions: The Naranjo algorithm was a useful tool to reduce the underreporting of ADRs. Events were common, but were associated with low morbidity and were reversible upon discontinuation of drug treatment. Moreover, there were no fatal events; therefore, benznidazole treatment was considered safe.