Objective: The study examined associations between sociodemographic factors and first-time use of mental health services by children and adolescents, including whether the patterns differ by age at first treatment contact. Methods: The authors examined sociodemographic characteristics of 4,949 youths listed on a psychiatric case register in Monroe County, New York who were under age 19 when first seen for public mental health treatment between 1987 and 1989. Data on race and type of insurance for patients in the county's four catchment areas were compared, with 1980 census data. Insurance was categorized as public (such as Medicaid) or private and was used as a proxy for socioeconomic status. Results: Both minority and publicly inspired-youths of low socioeconomic status were over-represented in the treatment population in relation to their numbers in the county, although publicly insured youths from the poorest catchment area were under-represented in the treatment population. Among children (ages five to 12) in the treatment population, males out numbered females by 2 to 1, but among adolescents (ages 13 to 18), the numbers were similar. Among minority groups, children receiving first-time mental health services were more likely to have public insurance. Minority adolescents were somewhat more likely to be privately than publicly insured.