Shigella sonnei causes approximately 10,000 cases of gastroenteritis each year in the United States. These infections occur predominately among young children and usually are associated with poor hygienic conditions in child-care settings. Outbreaks of shigellosis among men who have sex with men (MSM) have occurred because of direct or indirect oral-anal contact but usually are caused by Shigella flexneri. This report describes an investigation of S. sonnei cases that occurred among MSM in San Francisco during May-December 2000. Following efforts to heighten awareness, the number of cases has declined, but new cases continue to occur at low levels in this risk group (Figure 1). The increased incidence of sexually transmitted Shigella and other sexually transmitted diseases (STDs) in MSM require renewed and innovative prevention efforts.