Objective: To explore long-term trends in height, weight and body mass index (BMI) across birth cohorts among Indian women aged 15-30. Design: Nationally representative cross-sectional surveys. Setting: Data from three National Family Health Surveys conducted in 1998-99, 2005-06 and 2015-16. Height and weight were modeled jointly, employing a multivariate regression model with age and birth cohorts as explanatory variables. The largest birth cohort (born 1988-92) was the reference cohort. Stratified analyses by place of residence and by marital status and dichotomized parity were also performed. Participants: 437,753 non-pregnant women aged 15-30 years. Results: The rate of increase in height, weight and BMI differed across birth cohorts. The rate of increase was much lower for height than weight, which was reflected in an increasing trend in BMI across all birth cohorts. In the stratified analyses, increase in height was found to be similar across urban and rural areas. Rural women born in the latest birth cohort (1998-2001) were lighter, whereas urban women were heavier compared to the reference cohort. A relatively larger increase in regression coefficients were observed among women born between 1978-82 compared to women born between 1973-77 when considering unmarried and nulliparous ever-married women and, one cohort later (1983-87 vs. 1978-82), among parous ever-married women. Conclusion: As the rate of increase was much larger for weight than for height, increasing trends in BMI were observed across the birth cohorts. Thus, cohort effects show an important contributory role in explaining increasing trends in BMI among young Indian women.