The aim of the present study was to describe postpubertal changes in total and abdominal adiposity in young men and the relation to changes in physical activity (PA). The study included 107 white men with a mean age of 17.1 +/- 1.7 years at baseline. Total percentage body fat (%BF) and abdominal percentage body fat (abd%BF) were measured at baseline and after a mean time of 28, 68, and 92 months using dual-energy X-ray absorptiometry (DXA). PA (h/week) was assessed at each visit by questionnaire. Over the study period, significant increases of 7.8 +/- 5.5%BF and 9.0 +/- 5.6 abd%BF were observed. Subjects who were active athletes throughout the study (n = 24), or nonathletes not changing their level of PA during follow-up (n = 27) increased 5.7 +/- 3.2 and 8.1 +/- 6.7%BF, respectively. Athletes who quit organized training during follow-up period (n = 56) increased by 8.7 +/- 4.9%BF. In the total cohort, the average annual gains in BMI, %BF, and abd%BF were 0.4 kg/m(2), 0.9%BF, and 1.1abd%BF (all P < 0.0001), respectively. Adjustment for changes in PA altered the coefficient magnitudes only marginally. Changes in PA were, however, significantly and inversely associated with changes in %BF and abd%BF (P = 0.005 and P = 0.02, respectively), but were not significantly associated with BMI development (P = 0.15). In summary, our results indicate that the natural course of adiposity development in postpubertal men is characterized by adiposity gains. The influence of PA on especially abd%BF may influence the future risk of cardiovascular disease.