During 1987, four New York State summer camps for the mentally retarded and developmentally disabled experienced outbreaks of Shigella sonnei gastroenteritis. Cases occurred in 150 of 286 (attack rate (AR) = 52%), 167 of 295 (AR = 57%), and 25 of 114 (AR = 22%) persons in three camps, respectively; a fourth camp reported eight cases. Epidemiologic investigation suggested point-source foodborne outbreaks in two camps, while person-to-person spread appeared to predominate in the other two. Numerous secondary cases were identified among contacts outside the facilities in the second and third camps. To quantify the extent of the problem, the authors reviewed data on 77 infectious disease outbreaks (12 in camps for the handicapped and 65 in camps for the nonhandicapped) that occurred in the 12,484 registered camp sessions (316 for the handicapped and 12,168 for the nonhandicapped) held during the six-year period 1982-1987. Camps for the handicapped demonstrated approximately a seven times greater risk for all types of infectious disease outbreaks (AR = 38 outbreaks/1,000 camp sessions vs. five outbreaks/1,000 camp sessions; relative risk (RR) = 7.1, 95% confidence interval (CI) 3.9-13.0), including those of gastrointestinal etiology (RR = 8.6, 95% CI 4.4-16.8) and those due to Shigella (RR = infinity). Large camp size (RR = 2.3, 95% CI 1.3-4.1) and long duration of camp sessions (RR = 3.9, 95% CI 1.3-11.6) also increased the risk for outbreaks; however, this risk was predominantly in the camps for the nonhandicapped--other factors relating to personal hygiene and close camper-staff contact were probably more important in the camps for the handicapped. These outbreaks demonstrate the impact of shigellosis at summer camps for the mentally retarded and the need for early preventive action.