We evaluated the effect of repeated microwave irradiation on soft contact lens parameters to determine if microwave disinfection affects soft lens polymers or parameters. Ten factory-sealed lenses from each of the four FDA categories were placed in Ciba AOsept cases which were filled with 13 ml of sterile unpreserved saline. The cases were placed in a 10-cm diameter circle on the rotating plate of a standard 2450 MHz 650 W microwave oven and exposed to repeated 5-min cycles of microwave irradiation. The lens parameters, including back vertex power, back optic zone radius, diameter, thickness and water content, were measured over a period of 200 cycles to simulate over 6 months of daily disinfection. The postirradiation measurements were compared to baseline measurements taken before microwave exposure. We found statistically significant changes in many lens parameters, but all were small and few were clinically significant. These findings indicate that microwave disinfection does not have a clinically significant effect on the parameters of most unworn soft contact lenses. Further studies are needed to determine the long-term effects of microwave disinfection on worn soft contact lenses.