To evaluate the efficacy and safety of valsartan (V) or chlorthalidone (C) monotherapy in comparison with a fixed combination of valsartan and chlorthalidone (V + C).This 12-week multicenter randomized three-arm open-label study randomly allocated 72 patients to V or C as monotherapy or a combination of V + C. The aim was to measure changes in office systolic blood pressure (SBP) and diastolic blood pressure (DBP) and in 24-hour ambulatory blood pressure monitoring (ABPM) from baseline to week 12, in addition to medication tolerability.The proportion of patients achieving target BP in office at week 12 was not statistically different for the three groups. However, comparisons of daytime and nighttime 24-hour ABPM values from baseline to week 12 revealed significant differences in nighttime mean SBP for the three groups, due to a significantly greater reduction in the values in patients assigned to the V + C group (-14.7 vs. -8.7 vs. -10.7, P = .042, V+C; V; C, respectively). Although patients assigned to the V + C group also had greater nighttime reduction in mean DBP values compared with those in the other groups, this difference was not statistically significant. The incidence of adverse events did not differ significantly.In patients with hypertension treated with V, C, and both medications combined, the fixed combination of V + C provided a significantly greater reduction of late night to early morning BP values when interventions were assessed with 24-hour ABPM.clinicaltrials.gov Identifier: NCT.01850160, https://clinicaltrials.gov/ct2/show/NCT01850160.