Surveillance for toxic-shock syndrome (TSS) in Wisconsin detected 38 cases with onsets from September 1975 through June 1980. Thirty-seven of the cases occurred after January 1, 1979; 37 of the patients were women, 35 cases occurred during menses; 38 patients were white; and one patient died. Cervical or vaginal cultures were obtained before antibiotic therapy in 23 patients, and 17 cultures were positive for Staphylococcus aureus. Ten patients had at least one recurrent episode during subsequent menstrual periods. The recurrence rate was lower in patients who had been treated with beta-lactamase-resistant antibiotics. Thirty-five patients were matched for age and menstruation to 105 controls: 34 of 35 cases (versus 80 of 105 controls) used tampons during every menstrual period (P < 0.01); nine of 35 cases (versus 64 of 105 controls) practiced contraception (P < 0.001). In Wisconsin the minimum incidence of TSS as defined by clinical criteria is 6.2 cases per 100,000 menstruating women per year. The rate of TSS among menstruating women younger than 30 years was 2.4 to 3.3 times the rate among those who were 30 or older.