Resting pulmonary arterial pressure increases with age in humans. In the general population, higher values are associated with increased mortality, and in common cardiopulmonary diseases, such as congestive heart failure and chronic obstructive pulmonary disease, the presence of pulmonary arterial hypertension portends a worse outcome. Pulmonary arterial pressure increases during alveolar hypoxia, as a consequence of constriction in the pulmonary vasculature. We hypothesized that older men have more vigorous hypoxic pulmonary vasoconstriction than younger men. Twelve younger (20.5 ± 0.5 years old) and nine older men (55.8 ± 2.1 years old) were exposed for 20 min on different days to isocapnic hypoxia (end‐tidal  = 50 mmHg) and isocapnic euoxia (end‐tidal  = 100 mmHg); each was preceded (baseline) and followed by 5 min of isocapnic euoxia. Systolic pulmonary arterial pressure and cardiac output were measured continuously using Doppler echocardiography. Systolic pulmonary arterial pressure was greater during baseline euoxic measurements in older participants (27.8 ± 0.8 versus 24.1 ± 0.7 mmHg, P = 0.001) and also increased more during hypoxia in older participants (15.2 ± 1.3 versus 9.6 ± 0.9 mmHg, P = 0.011). Cardiac output did not differ between the two groups during baseline measurements (P = 0.60) or hypoxia (P = 0.49). All data are means ± SEM. The increased magnitude of hypoxic pulmonary vasoconstriction demonstrated with age has implications for individuals wishing to ascend to high altitude or travel by air, for those suffering from conditions in which global alveolar hypoxia is a feature and for patients requiring general anaesthesia.