We reviewed case records for 583 juvenile delinquency intakes in four county juvenile probation offices; 14.4% were receiving mental health or substance use services at case opening, and 24.9% were newly identified during probation contact. Youths were significantly more likely to be newly identified if they were repeat offenders, if their probation officer knew more about mental health and if they resided in a county without a shortage of available mental health professionals. Probation officers were especially likely to underidentify internalizing disorders. Policy implications for promoting identification of mental health needs and improving linkage to community service providers are discussed.