Conduct disorder (CD) prior to age 15 identifies a subgroup of men with severe mental illness (SMI) who present a high risk for violence that persists across the life span. The present study examined male violent offenders with SMI in a forensic hospital in Spain, comparing those with SMI+CD and those without SMI-CD on the HCR-20 and PCL: SV. Violent offenders with SMI+CD obtained higher HCR-20 and PCL: SV total scores, and much higher H and factor 2 scores as compared to those without prior CD. Men with SMI+CD present a challenge to forensic psychiatric services.