The present study examined the longitudinal impact of Project P.A.T.H.S. (Positive Adolescent Training through Holistic Social Programmes) on adolescent developmental outcomes in Hong Kong. Using a longitudinal randomized group design, seven waves of data were collected from 24 experimental schools (n=4049 at wave 1) in which students participated in the Tier 1 Program of Project P.A.T.H.S. and 24 control schools (n=3797 at wave 1). Results based on individual growth curve modeling generally showed that, relative to the control participants, participants in the experimental group had: (a) a higher level of positive development; (b) a lower level of substance abuse; and (c) a lower level of delinquent behavior. Participants who regarded the program to be beneficial also showed higher levels of positive development and lower levels of problem behavior than did the control school students. The present findings suggest that Project P.A.T.H.S. is effective in promoting positive development and preventing adolescent problem behavior in Chinese adolescents in Hong Kong.