Background. There are currently limited data on whether the effect of spironolactone in patients with resistant arterial hypertension depends on age and sex. Methods. Patients with an office systolic blood pressure (BP) >140 mmHg or diastolic BP >90 mmHg, despite treatment with at least 3 antihypertensive drugs including a diuretic, were randomly assigned to receive spironolactone or a placebo for 8 weeks in a double-blind, placebo-controlled, multicentre trial (ASPIRANT). Results. Analyses were done on 55 patients treated with spironolactone and 56 patients treated with placebo. Significant reductions of office systolic BP (-8.9 ± 6.7 mmHg, P=0.012), 24-h ABPM systolic BP (-7.9 ± 7.2 mmHg, P=0.032) and ABPM day-time systolic BP (-7.5 ± 7.1 mmHg) after 8 weeks of spironolactone treatment, compared to placebo, were only observed in patients with a median age >62 years. The office and ABPM systolic BP reductions in patients aged ≤62 years and diastolic BP reductions by spironolactone in both age groups were not significant compared to placebo. Women tended to have a nonsignificantly higher reduction in systolic BP with spironolactone treatment, and there was no difference in diastolic BP reduction between women and men. Conclusions. S pironolactone only leads to a reduction of systolic BP in older patients with resistant arterial hypertension aged >62 years, and is effective to a similar extent in men and women.