The optimal therapy for infections due to Nocardia species has not been established. To assess the efficacy of trimethoprim-sulfamethoxazole (TMP-SMX), we reviewed the records of 19 patients with Nocardia infections seen at Duke University Medical Center, Durham, NC, who were treated with this drug, either alone or in combination with other antibiotics or a surgical procedure. Underlying diseases or therapy causing immunosuppression were present in all but five cases. Sites of involvement were lung (ten of 19), wound (two of 19), and brain (two of 19); five of 19 patients had disseminated disease. The mean duration of therapy was 7.2 months. Overall cure or improvement was achieved in 89% (17/19) of cases; 80% of patients with disseminated disease and 60% of those with CNS involvement recovered. This experience, and accumulated clinical evidence in the literature, indicates that TMP-SMX should be considered the therapeutic drug of choice in infections due to Nocardia species.