In a simultaneous community and nosocomial (hospital-based) epidemic of keratoconjunctivitis lasting one year, 97 patients had clinical findings characteristic of EKC. Seventy-one percent of the cases were confirmed by laboratory tests including viral isolation, antibody response detected by complement fixation and hemagglutination inhibition tests, or immunofluorescent detection of adenovirus antigen in conjunctival scrapings. The community epidemic was a mixed adenovirus type 19 and type 8 outbreak. The nosocomial outbreak was due primarily to adenovirus type 8 (91%). The epidemiologic data of the nosocomial epidemic were representative of the population involved. The community outbreak was primarily in young individuals between 11 and 40 years of age. The secondary household attack rates were 20% and essentially were equal in both epidemics. The primary mode of spread in the nosocomial outbreak was by contamination of the examiner's fingers. In the community epidemic the mode of spread was believed to be close personal contact in a young and active age group.