Free testosterone was measured in the saliva of 89 male prison inmates. Inmates with higher testosterone concentrations had more often been convicted of violent crimes. The relationship was most striking at the extremes of the testosterone distribution, where 9 out of 11 inmates with the lowest testosterone concentrations had committed nonviolent crimes, and 10 out of 11 inmates with the highest testosterone concentrations had committed violent crimes. Among the inmates convicted of nonviolent crimes, those higher in testosterone received longer times to serve before parole and longer punishments for disciplinary infractions in prison. In the housing unit where peer ratings were most reliable, inmates rated as tougher by their peers were higher in testosterone.