Whole blood serotonin was measured in a representative birth cohort of 781 21-year-old men & women. Violence was measured using conviction records & subjects’ self-reports. Potential intervening factors including suicide attempts were addressed. Whole blood serotonin related to violence among men but not women. The 9 men who attempted suicide did not differ significantly from nonsuicidal men on serotonin level. Violent men were 6.16 times more likely to attempt suicide than the nonviolent men.