A case-control study was used to evaluate the relative risk (RR) of acute contact lens-related disorders. The study sample comprised new patients wearing contact lens presenting at the accident and emergency department at Moorfields Eye Hospital, London, England, in 12 months. Disorders were classified by pathogenesis. Compared with gas-permeable hard contact lenses (the referent), extended-wear soft contact lenses were related to the largest overall RR for any complication (2.7 [95% confidence limits, 1.73, 4.16]), whereas for daily wear soft contact lenses the overall RR was 1.3 (confidence limits, 1.0, 1.72). Relative risks were greatest for extended-wear soft contact lens wearers with metabolic disorders (2.1 [confidence limits, 1.28, 3.4]) and for such wearers with sterile infiltrates (2.4 [confidence limits, 1.22, 4.84]). Among those using daily wear contact lenses, RR was highest for those with toxic/hypersensitivity disorders (5.9 [95% confidence limits, 3.27, 10.49]). Severe complications involving greater morbidity occurred more frequently with extended-wear soft contact lenses. This could be reduced by selecting a more appropriate lens type to correct low refractive errors.