Five hundred and eighty-six phakic retinal detachments were studied to characterize the features of 111 cases with a history of trauma and to establish improved guidelines for medico-legal determinations. Twenty-eight percent of contusion detachments were myopic, nine times higher than expected. Myopes typically developed giant tears and nasal dialyses (p less than 0.001); emmetropes developed inferotemporal dialyses (p less than 0.005). Lattice degeneration did not increase post-traumatic detachments risk. Dialyses and giant tears caused 69% of traumatic detachments and 6% of nontraumatic detachments (p less than 0.001). Forty-seven percent of contusion detachments had no late objective evidence of trauma. Five percent of detachments with a history of trauma were not caused by trauma (false positives).