OBJECTIVE: Although there is evidence for the association between air pollution and decreased lung function in children, evidence for adolescents and young adults is scarce. For a peri-urban area in India, we evaluated the association of ambient PM2.5 and household air pollution with lung function for young adults who had recently attained their expected maximum lung function. METHODS: We measured, using a standardized protocol, forced expiratory volume in the first second (FEV1) and forced vital capacity (FVC) in participants aged 20-26 years from the third follow-up of the population-based APCAPCS cohort (2010-2012) in 28 Indian villages. We estimated annual average PM2.5outdoors at residence using land-use regression. Biomass cooking fuel (a proxy for levels of household air pollution) was self-reported. We fitted a within-between linear-mixed model with random intercepts by village, adjusting for potential confounders. RESULTS: We evaluated 1,044 participants with mean age of 22.8 (SD = 1) years (range 20-26 years); 327 participants (31%) were female. Only males reported use of tobacco smoking (9% of all participants, 13% of males). The mean ambient PM2.5 exposure was 32.9 (SD = 2.8) µg/m3; 76% reported use of biomass as cooking fuel. The adjusted association between 1 µg/m3 increase in PM2.5 was -27 ml (95% CI, -89 to 34) for FEV1 and -5 ml (95% CI, -93 to 76) for FVC. The adjusted association between use of biomass was -112 ml (95% CI, -211 to -13) for FEV1 and -142 ml (95% CI, -285 to 0) for FVC. The adjusted association was of greater magnitude for those with unvented stove (-158 ml, 95% CI, -279 to -36 for FEV1 and -211 ml, 95% CI, -386 to -36 for FVC). CONCLUSIONS: We observed negative associations between ambient PM2.5 and household air pollution and lung function in young adults who had recently attained their maximum lung function.