The channels contributing to the intergenerational correlation in body mass are not well understood. A novel decomposition approach from quantitative genetics is used to estimate the contribution of maternal characteristics, household income, and adolescent behaviours on the intergenerational correlation in BMI. The analysis uses data on mothers and their adolescent children from the British Household Panel Survey. The overall intergenerational correlation in BMI is 0.25. Maternal educational attainment and adolescent participation in daily physical activity are the largest contributing factors to the intergenerational correlation in BMI. Maternal employment and high daily television viewing by the adolescent are also contributing factors. Overall, observable characteristics explain 11.2% of the intergenerational correlation in BMI.