In this double-blind, placebo-controlled, randomised, parallel-group study, a combination tablet of candesartan cilexetil/hydrochlorothiazide (HCTZ), 16/12.5 mg once daily, reduced sitting diastolic blood pressure (DBP) significantly more (p = 0.037) than candesartan cilexetil/placebo, 16 mg once daily, in patients with mild to moderate primary hypertension (n = 328) who had not reached target blood pressure with candesartan cilexetil, 16 mg once daily. Ar the end of the 8-week double-blind treatment period, the adjusted mean reductions in sitting DBP, 24 h post dose, were 7.5 mm Hg in the candesartan cilexetil/HCTZ treatment group and 5.5 mm Hg in the candesartan cilexetil/placebo treatment group, corresponding to an adjusted mean difference between treatments of 2.0 mm Hg in favour of candesartan cilexetil/HCTZ (95% CI 0.1-3.8 mm Hg, p = 0.037). The adjusted mean reductions in sitting systolic blood pressure, 24 h post dose, were 12.0 mm Hg and 7.5 mm Hg, respectively, corresponding to an adjusted mean difference between treatments of 4.5 mm Hg (95% CI 1.1-8.0, p = 0.01). Consistent with the placebo-like tolerability of candesartan cilexetil reported in other studies, both treatments were very well tolerated, with a similar pattern and low frequency of adverse events in both treatment groups.