An unusually large outbreak of conjunctivitis caused by adenovirus type 4 involved 113 proved cases during a 7-month period. Though the disease was less severe than is commonly seen in epidemic keratoconjunctivitis caused by other serotypes, the cornea was affected in 23% of cases and symptoms persisted for at least 5 weeks in 6 patients. A concurrent increase in nonocular adenovirus type 4 infections in the Bristol area was not observed. Nine of the cases could have arisen as a result of hospital cross-infection.