The YSC is a delinquency prevention program (affiliated with the South Philadelphia Community Center (SPCC)) for the area youths between the ages 10 and 18 who have been arrested and are in the process of entering the juvenile justice system, or are deemed troublesome by other agencies or by their families. Program influence was judged by an estimated decrease in the rates of juvenile arrests after the implementation of the Center in 1975 in the two police districts within the target area. Uniform Crime Reports (UCR) and the Center's caseboard data were used to determine arrest fluctuations. Philadelphia census tract data described the demographic characteristics and trends of the area and identified possible intervening ecological factors affecting arrest rates. The results showed a 26 percent decrease in the number of arrests in focal area from 1976 to 1977. However, several other factors could have been responsible for the decline, including the current policy limiting status offender arrests, the 15 percent decrease in overall city crime rates, a police crackdown on gang fighting, and the presence of other youth service agencies. There were also difficulties in the interpretation of the data, such as the relationship between arrest and remedial rates, and the use of official data only, which ignores the interactive effects of age. Despite these weaknesses this methodology is useful for examining a service center's area impact on official arrests. Future evaluation efforts should emphasize more accurate means for assessing the effects of demographic factors upon arrest rates. Statistical data, notes, and references are included.