The Portland Youth Aid Bureau grew out of the Portland Model Cities Program of the late 1960's and was designed to reduce or prevent delinquency. The bureau's staff consists of 17 sworn police officers and a small number of civilian support personnel. Official data and interviews were used as the basis for assessing the bureau's success in reducing juvenile court referrals by the police, reducing delinquency, reducing recidivism, and improving attitudes and relationships between juveniles and youth aid bureau officers. Findings showed that although court referrals increased in Portland due to the extremely low baseline level of referrals, referrals for the entire State have declined since the establishment of youth aid bureaus. Data on recidivism are inadequate and inconclusive. Although overall delinquency rates continue to rise in Portland, they may have risen even more rapidly if a bureau had not been established. Major reductions have apparently been achieved in shoplifting and vandalism, the only areas in which specific strategies have been developed and intensively applied. In all other offense types, referral rates are either flat or rising. Attitudes and relationships between youths and officers are reported as consistently improved following the inauguration of youth aid bureau activities. Findings indicate that the youth aid bureau concept is an important addition to criminal justice thought and practice and can be implemented in virtually any police department. An in-house program of both descriptive and evaluative research should be established, with emphasis on developing meaningful data. Tables, footnotes, and 10 references are provided.