Adiposity and inactivity have been associated with increased risk of hypertension. However, reports on the joint effect of these two risk factors in relation to hypertension are scarce and their interaction poorly understood. We prospectively examined both independent and joint effects of measured body mass index (BMI) and self-reported physical activity on the risk of hypertension. We conducted a longitudinal study of 11,238 men and 15,301 women who participated in the Nord-Trøndelag Health Study (HUNT) in Norway. Poisson regression was used to estimate adjusted risk ratios (RRs) of hypertension (≥140/90 mmHg) according to BMI and physical activity. BMI was positively associated with risk of hypertension in both sexes (Ptrends < 0.001), whereas the independent effect of physical activity was less clear. Obese men who reported no physical activity had a RR of 1.50 (95% confidence interval (CI): 1.27-1.77) compared to normal weight men with a high activity level, whereas obese men who reported high activity levels had a RR of 1.16 (95% CI: 0.79-1.70). Correspondingly, obese and inactive women had a RR of 1.55 (95% CI: 1.35-1.77), whereas obese and highly active women had RRs of 1.41 (95% CI: 1.18-1.69). Our data suggest that high levels of physical activity could to some extent attenuate the unfavorable effect of adiposity on hypertension, particularly in men.