The objective of this case-control study of idiopathic retinal detachment was to evaluate previously suggested hypotheses about risk factors for retinal detachment and to investigate whether new ocular or systemic risk factors could be identified. Between 1986 and 1990, data were obtained at five US clinical centers on 253 patients with idiopathic retinal detachment and 1,138 controls. Patients with pathologic myopia were excluded. Data were collected from interviews, clinical examinations, and laboratory analyses of blood samples. Only one clearly relevant risk factor, myopia, emerged from the analyses. An eye with a spherical equivalent refractive error of -1 to -3 diopters had a fourfold increased risk of retinal detachment compared with a nonmyopic eye; if the refractive error was greater than -3 diopters, the risk was increased 10-fold. The data suggest that almost 55% of nontraumatic detachments in eyes without previous surgery are attributable to myopia. The etiology of retinal detachment appears to be related to the architecture of the eye. The study found no evidence that systemic factors, particularly cardiovascular factors, play a role.