Abstract: A dosimeter monitors the ultraviolet radiation exposure of a body and provides an alarm when the cumulative radiation exposure attains a threshold level which is variable depending on the accumulated exposures of the body. A detector generates a sensing signal proportional to the intensity of ultraviolet radiation impinging the body. A first function of the sensing signal is integrated with respect to time to generate an active signal representative of the accumulated dose of radiation received by the body having regard to the intrinsic tolerance of the body. A second function of the sensing signal is integrated with respect to time to generate a reference signal representative of the optimal dose of accumulated radiation which is desired. An alarm is generated when the active signal magnitude attain the reference signal magnitude.