The epidemiology & genetics of suicidal thoughts & behavior was studied in twins. The twins were surveyed on a variety of topics including suicidality, mental illnesses & life events. Associations between familial influences, psychiatric history & traumatic events on suicidality were found. Social & psychiatric factors were more powerful predictors of suicidality than genetics, although suicidal behavior in a respondent’s co-twin was still a powerful predictor in monozygotic pairs. (72 refs.)