Left ventricular hypertrophy is a strong predictor of prognosis in hypertension. Physical activity is associated with higher left ventricular mass but also reduced risk of cardiovascular outcomes. The aims were to explore whether (1) presence of hypertension modifies the association between physical activity and left ventricular mass; (2) the beneficial association between physical activity and prognostic outcome is modified by left ventricular hypertrophy. Randomly selected number of 3078 persons from the general population underwent echocardiogram. Left ventricular mass was indexed to body surface area. Level of physical activity was self-reported: inactivity, light activity, and moderate/high activity. Blood pressure was measured in rest: normal BP (<140/90 mm Hg) and hypertension (≥140/90 mm Hg or in pharmacological treatment for hypertension). Presence of hypertension modified the association between physical activity and left ventricular mass index significantly (test for interaction: P=0.01): in normal BP, higher levels of physical activity were associated with significantly higher left ventricular mass index (P<0.001), but this was not present in hypertension (P=0.90). Level of physical activity was associated with reduction in mortality and cardiovascular outcome independent of the presence of LVH (Persons with LVH: light activity HR, 0.77 [0.52-1.15], moderate/high activity HR, 0.61 [0.38-0.97]; test for interaction between LVH and level of physical activity P=0.71). In conclusion, persons with normal BP had higher left ventricular mass index at increased levels of physical activity, whereas this association was not present among persons with hypertension. Level of physical activity was associated with better prognosis independent of whether left ventricular hypertrophy was present or not.