This longitudinal study aimed to identify individual and environmental predictors of adolescents' sports participation and to examine whether availability of sports facilities moderated the intention-behaviour relation. Data were obtained from the ENvironmental Determinants of Obesity in Rotterdam SchoolchildrEn study (2005/2006 to 2007/2008). A total of 247 adolescents (48% boys, mean age at follow-up 15 years) completed the surveys at baseline and follow-up. At baseline, adolescents completed a survey that assessed engagement in sports participation, attitude, subjective norm, perceived behavioural control and intention towards sports participation. Availability of sports facilities (availability) was assessed using a geographic information system. At follow-up, sports participation was again examined. Multiple logistic regression analyses were conducted to test associations between availability of sports facilities, theory of planned behaviour variables and the interaction of intention by availability of sports facilities, with sports participation at follow-up. Simple slopes analysis was conducted to decompose the interaction effect. A significant availability × intention interaction effect [odds ratio: 1.10; 95% confidence interval: 1.00-1.20] was found. Simple slopes analysis showed that intention was more strongly associated with sports participation when sports facilities were more readily available. The results of this study indicate that the intention-sports participation association appears to be stronger when more facilities are available.