Introduction: Governador Valadares is an endemic area of American tegumentary leishmaniasis (ATL). The detection rate was 15.36 per 100,000 habitants from to 2006(Miranda, 2008. This study aimed to analyze the effects of age on the frequency of adverse reactions caused by antimony in the treatment of ATL in the City of Governador Valadares, State of Minas Gerais, Brazil, during 2009. Methods: Data were collected from the forms of the Information System for Notifiable Diseases, and from charts, questionnaires, and home visits to patients. Results: The study included 40 patients, 26 (65%) of whom were males. Individuals over the age of 50 had a 66% higher rate of adverse effects than subjects who were 50 years old or less (CI 95%, 1.14-2.41). The average age of individuals who reported some type of adverse effect was 44.11 years (SD = 20.14), while the average age of the group that did not report any adverse effect was of 25.46 years (SD = 18.37; p < 0.01). Clinical healing was 67.5%, and 10% of patients discontinued the treatment. Conclusions: In the treatment of ATL, the age of patients should be considered, because most adverse reactions occur in individuals over 50 years of age. For this reason, the drug should be used with restriction in these cases.