The purpose of this study was to examine (a) whether adolescents' leisure-time sports participation is socially stratified, and (b) whether possible stratification patterns have changed over the last decades. The population for the study consisted of four random samples of high school boys and girls in Flanders who were exposed to a standardized questionnaire in 1969, 1979, 1989 or 1999. The results indicated that social back ground variables remain relevant to analyse constraints on leisure-time sports participation. Parental sports participation, gender and school programme still determine the respondents' active involvement in sports. The impact of gender and school programme has intensified during the last decade. On the other hand, the adolescents' sports participation is no longer correlated with the socioeconomic status of the parents. Some explanations are discussed for linking the adolescents' sports participation behaviour to the respondents' social background. (Contains 8 tables, 2 figures and 6 notes.)