The clinical and microbiological features of 31 cases of mycetoma seen in 8 years at a Riyadh hospital are described. Eighteen were due to Streptomyces somaliensis, 10 to Madurella mycetomatis and one each to Actinomadura madurae, Nocardia asteroides, and an unidentified species of Cladosporium. No immune defects were detected in the patients. Eleven had osteolytic lesions and 17 required surgery. Only seven patients were cured. Streptomyces infections were seen from all parts of Saudi Arabia outside the Rub Al Khali, but Madurella occurred mostly in highland regions where rainfall is higher.