This study aims to empirically identify age of onset groups and their clinical and background characteristics in forensic patients with schizophrenia. Hospital charts were reviewed of all 138 forensic patients with schizophrenia admitted to Geha Psychiatric Hospital that serves a catchment area of approximately 500,000 people, from 2000 to 2009 inclusive. Admixture analysis empirically identified early- (M=19.99, SD=3.31) and late-onset groups (M=36.13, SD=9.25). Early-onset was associated with more suicide attempts, violence before the age of 15, and early conduct problems, whereas late-onset was associated with a greater likelihood of violence after the age of 18 and marriage (P<0.01). The current findings provide clinicians with a unique direction for risk assessment and indicate differences in violence between early- and late-onset schizophrenia, particularly co-occurrence of harmful behavioral phenotypes.