The multiple chemical sensitivities (MCS) syndrome is characterized by unexplained physical and psychiatric complaints attributed by patients and some of their physicians to low-level chemical exposures. In this study, we interviewed 15 subjects with MCS and 21 controls about their first-degree relatives using the Family History-Research Diagnostic Criteria (FH-RDC). Subjects with MCS were more likely than controls to report their relatives to have major depression, alcoholism, panic disorder, obsessive-compulsive disorder, and antisocial personality disorder. They were also likely to have past suicide attempts, and to have received some form of psychiatric treatment (hospitalization, medication or electroconvulsive therapy, or counseling). Nearly 30% of the relatives of subjects with MCS were reported to have MCS themselves. Possible reasons for the findings are discussed.