Despite many imperfections in the nationwide reporting of toxic shock syndrome, the available data provide some useful information. The crude toxic shock morbidity rate has been estimated as approximately 0.50 per 100 000 United States population per year. This morbidity rate exceeds those for paralytic poliomyelitis, tetanus, tularemia, diphtheria, and typhoid fever, and is about one half of the rate for meningococcal infections and pertussis. The estimate of 8.9 cases of toxic shock syndrome per 100 000 menstruating women is similar to the crude rates for primary and secondary syphilis and mumps. From these comparisons, the incidence of toxic shock syndrome does not appear as low as some might suppose.