Severe acute respiratory syndrome (SARS) was first recognized in Toronto in a woman who returned from Hong Kong on February 23, 2003 (1). Transmission to other persons resulted subsequently in an outbreak among 257 persons in several Greater Toronto Area (GTA) hospitals. After implementation of provincewide public health measures that included strict infection-control practices, the number of recognized cases of SARS declined substantially, and no cases were detected after April 20. On April 30, the World Health Organization (WHO) lifted a travel advisory issued on April 22 that had recommended limiting travel to Toronto. This report describes a second wave of SARS cases among patients, visitors, and health-care workers (HCWs) that occurred at a Toronto hospital approximately 4 weeks after SARS transmission was thought to have been interrupted. The findings indicate that exposure to hospitalized patients with unrecognized SARS after a provincewide relaxation of strict SARS control measures probably contributed to transmission among HCWs. The investigation underscores the need for monitoring fever and respiratory symptoms in hospitalized patients and visitors, particularly after a decline in the number of reported SARS cases.