The search for nongenetic factors that mediate the expression of a genetic vulnerability to Tourette's syndrome (TS) is an important undertaking that may provide valuable clues concerning the pathophysiology of this disorder as well as potential treatment approaches. In a direct interview study, the perinatal experiences of 31 TS patients were compiled in an effort to identify risk factors associated with tic severity. Severity of maternal life stress during pregnancy, gender of the child, and severe nausea and/or vomiting during the first trimester were found to be significantly associated with current tic severity. Future longitudinal studies of "at-risk" children are needed to confirm these findings. Set in the context of a known chromosomal site for the TS diathesis, such studies will permit the identification and quantification of risk and protective factors in the expression of TS and further develop TS as a model neuropsychiatric disorder for the study of gene-environment interactions.