To investigate whether level of prematurity (very, moderate, late preterm, vs full term) is associated with physical activity from childhood to adolescence and to identify factors in childhood that predict moderate-vigorous physical activity in early adolescence.

Parents reported on physical activity at the age 5, 7, and 11 years (n = 12 222-14 639) and adolescents self-reported on moderate-vigorous physical activity at 14 years (n = 10 974). At age 14 years, a subgroup was also assessed by wrist accelerometer (n = 4046).

Prematurity was associated with a small or no difference in physical activity at each time point. At age 14 years, moderate-vigorous physical activity in self-report and accelerometer was higher in male adolescents, those of white ethnicity, or higher parental education, having been taken to live sport events at age 5 or 7 years or having taken part in organized physical activity at 5 or 7 years.

In this representative national cohort study in the United Kingdom, preterm birth was not found to be associated with physical activity between 5 and 14 years. Organized physical activity and watching sport events early in life may increase moderate to vigorous physical activity in adolescents.