Seven cases of toxic shock syndrome has been reported to the Wisconsin Division of Health by 6 January 1980; all seven cases were in female patients, six of whom had onset of illness during active menstruation. Through passive reporting of cases by physicians and patients themselves, a total of 38 patients with confirmed cases of toxic shock syndrome had been identified by the Division of Health by 30 June 1980. Thirty-five patients with menstrual toxic shock syndrome were each age-matched to three menstruating control subjects as part of a case-control study to identify potential risk factors associated with menstrual toxic shock syndrome. Statistically significant findings included increased tampon usage by patients as compared with controls, and fewer patients than controls were using any method of birth control. Numerous other health and hygiene variables were examined and found not to be statistically significant. We critically review the potential biases inherent to the study design. The conclusions and experience gained in this study were crucial to the designing of later case-control studies.