Sulfadiazine is one of the drugs of choice in the treatment of paracoccidioidomycosis. Side effects are uncommon. Cutaneous and gastrointestinal reactions and rarely leucopenia and jaundice may occur. A patient on sulfadiazine 6 g daily exhibiting a good response is reported. On the 12th day, he presented an intense abdominal pain and reduced urinary output. An ultrasonography revealed diffuse calculosis in urinary tract. Peritoneal dialysis, urinary alkalinization and rehydration were instituted with complete restoration of renal function. This case illustrates the importance of an adequate hydratation of patients receiving sulfadiazine, a simple measure in the prevention of this uncommon complication which carries a high morbidity.