Between 1 January 1980 and 18 October 1981, investigators from the Centers for Disease Control collected information on 1407 cases of toxic shock syndrome using a nationwide passive surveillance system. Ninety-two percent of the reported cases were associated with menstruation. Information available on the type of menstrual device used shows that 99% of the cases occurred in tampon users. Menstrual cases occurred predominantly in whites (98%) under the age of 25 (65%). The case/fatality ratio for menstrual toxic shock syndrome was 3.1% for cases with onset in 1981. The distribution of reported cases by date of onset showed a gradual increase in the number reported before the summer of 1980, a sharp increase during the summer and early fall of 1980, a marked decrease in the late fall of 1980, and a subsequent gradual decrease. Factors affecting the incidence and reporting of toxic shock syndrome during these periods include changes in the number of tampon users, changes in the availability and usage patterns of tampons, changes in the prevalence of toxin-producing strains of Staphylococcus aureus, improved recognition of the syndrome, and publicity.