Ninety-nine (11.6%) of 850 phakic retinal detachment patients had bilateral detachments. The incidence of bilaterality was greater in nontraumatic detachments (13.4%) than traumatic detachments (3.8%). Patients were divided into two refractive classes: (1) myopic, containing refractive errors of -2.50 diopters or more, and (2) nonmyopic, containing all other refractive errors. The rate of bilaterality in nontraumatic detachments varied with refractive class and lattice degeneration: nonmyopic without lattice (8.1%), nonmyopic with lattice (14.2%), myopic without lattice (16.3%), and myopic with lattice (24.6%). Mean age in years at onset of the initial detachment varied with refractive class and lattice degeneration: nonmyopic without lattice (59.1), nonmyopic with lattice (55.8), myopic without lattice (49.2), and myopic with lattice (28.2). Lattice degeneration reduced the interval between detachments. Annual risks of fellow eye detachments were calculated for four groups: nonmyopic without lattice (0.12%), nonmyopic with lattice (0.95%), myopic without lattice (1.3%), and myopic with lattice (0.98%).