Results indicated that early onset offenders were over 40 times more likely than late onset offenders to develop into chronic offenders. Main findings indicated that offenders first arrested at age 14 years were the most chronic, versatile, and dangerous offenders. Offenders first arrested in middle childhood, while rare, had accumulated hundreds of career arrests by adulthood. Offenders first arrested at ages 16 or 17 years were more likely to be convicted of felonies and sentenced to prison while offenders first arrested at ages 14 or 15 years were the most violent offenders. The author points out, however, that the majority of offenders with involved criminal careers were not initially arrested until adulthood. Data included self-reported criminal histories obtained from pretrial services at a large urban jail in Colorado. Self-reported data on criminal activities were supplemented with official records from the Interstate Identification Index (III) system, for 500 adult career criminals. Variables under examination included legal seriousness, dangerousness, versatility, and career span. Data was analyzed using descriptive, Ordinary Least Squares regression, and negative binomial regression analyses. Tables, references