Background. Phlebotonics have beneficial effects on some symptoms related to chronic venous disease (CVD) of the lower limbs. The most commonly used one is diosmin, available in a pure semisynthetic form or as a micronized purified flavonoid fraction. Patients and Methods. The primary objective of this single-blind, randomized, parallel-group, prospective study was to assess the clinical noninferiority of nonmicronized diosmin 600 mg once daily (D-group) compared to micronized diosmin 900 mg plus hesperidin 100 mg once daily (D/H-group) over a 6-month treatment period. Adult patients with a symptomatic CVD of the lower limbs (C0-C3 grade; 20-60 mm on a 100 mm visual analog scale (VAS)) were included. The primary endpoint was the change (from baseline to last postbaseline value) of the intensity of the lower-limb symptoms on VAS. Results. 114 patients (mean age, 44.4 years; women, 90.4%) were randomized in the per-protocol analysis (D-group, n=57; D/H-group, n=57). Symptoms significantly improved in both groups with adjusted mean VAS changes of -24.9 mm (p<0.0001) in the D-group and -22.8 mm (p<0.0001) in the D/H-group, corresponding to approximately 50% reduction in basal symptom intensity. The difference between groups was -2.1 mm with an upper limit of one-sided 90% confidence interval equal to 1.0 mm for a noninferiority margin set at 20 mm (noninferiority demonstrated). Intent-to-treat analysis confirmed per-protocol analysis. Difficulty in swallowing the tablets (VAS) was significantly lower in the D-group compared to the D/H-group (9.4 mm and 54.7 mm at 6 months, respectively; p<0.0001). The overall safety of both study drugs was good. Conclusion. Nonmicronized diosmin 600 mg was proven to have a noninferior efficacy compared to micronized diosmin 900 mg plus hesperidin 100 mg, associated with greater ease in swallowing the tablet.