PURPOSE: To identify clinical characteristics that were associated with an increased incidence of endophthalmitis in eyes with penetrating ocular trauma. METHODS: In part 1, a retrospective analysis was performed on 258 consecutive patients with penetrating ocular trauma presenting to the Bascom Palmer Eye Institute between October 1987 and January 1991. In part 2 of the study, 28 consecutive patients with culture-proven endophthalmitis were identified from the Clinical Microbiology Registry from April 1987 through September 1987 and February 1991 through August 1993. Clinical variables were evaluated in each part for association with an increased risk of endophthalmitis. RESULTS: In part 1 of the study, endophthalmitis developed in 13 (5%) of the 258 patients. Endophthalmitis did not occur in eyes that had blunt injury. In those eyes with a lacerating injury, there was an increased relative risk of infection in eyes with disruption of the crystalline lens. This risk factor was found statistically significant by univariate and multivariate analysis. In part 2 of the study, lens disruption was present in 24 (86%) of 28 patients with culture-proven endophthalmitis. Of the 41 patients with infection from part I and part II, 22 (54%) achieved visual acuity of 20/ 400 or greater. Endophthalmitis caused by coagulase-negative staphylococci had the best visual outcome, with 7 (64%) of 11 patients obtaining visual acuity of 20/ 400 or greater. CONCLUSION: Lens disruption in eyes with penetrating trauma is a significant risk factor for the development of endophthalmitis. The prognosis for useful vision in eyes with posttraumatic endophthalmitis is best when infection is caused by less virulent organisms.