Severe acute respiratory syndrome (SARS) has only recently been described. We provide individual patient data on the clinical course, treatment and complications experienced by 14 front-line health care workers and hospital support staff in Toronto who were diagnosed with SARS, and we provide follow-up information for up to 3 weeks after their discharge from hospital. As part of the initial response to the SARS outbreak in Toronto, our health care centre was asked to establish a SARS unit for health care workers who were infected. Patients were admitted to this unit and were closely monitored and treated until they were well enough to be discharged. We prospectively compiled information on their clinical course, management and complications and followed them for 3 weeks after discharge. The 11 women and 3 men described here (mean age 42 [standard deviation [SD] 9] years) were all involved in providing medical or ancillary hospital services to patients who were later found to have SARS. Onset of symptoms in 4 of our patients who could clearly identify only a single contact with a patient with SARS occurred on average 4 (SD 3) days after exposure. For the remaining 10 patients with multiple patient contacts, symptom onset followed exposure by a mean of 3.5 (SD 3) days after their exposure. All patients were treated with ribavirin, and all patients received levofloxacin. Many experienced major complications. Dyspnea was present in 12 patients during their stay in hospital, and all developed abnormalities on chest radiograph; 3 patients developed severe hypoxemia (PaO(2) < 50 mm Hg). All patients experienced a drop in hemoglobin. Nine patients had hemolytic anemia. Three patients experienced numbness and tingling in their hands and feet, and 2 developed frank tetany. All 3 had magnesium levels that were less than 0.1 mmol/L. All patients recovered and were discharged home. At a follow-up examination 3 weeks after discharge (5 weeks after onset of illness), all patients were no longer weak but continued to become fatigued easily and had dyspnea on minimal exertion. For 5 patients, chest radiographs still showed residual disease. SARS is a very serious illness even in healthy, relatively young people. The clinical course in our patients, all of whom met the case definition for SARS (which requires pulmonary involvement), resulted in dyspnea and, in some individuals, severe hypoxemia. Severe hemolytic anemia may be a feature of SARS or may be a complication of therapy, possibly with ribavirin.