In this study we report the first results from the largest cohort to date of newly diagnosed adult ITP patients randomized to treatment with dexamethasone alone or in combination with rituximab. Eligible were patients with platelet counts ≤ 25 x10(9)/L or ≤ 50 x10(9)/L with bleeding symptoms. 133 patients were randomly assigned to either dexamethasone monotherapy 40 mg/day for 4 days (n=71) or in combination with rituximab 375 mg/m(2) weekly for 4 weeks (n=62). Patients in both groups were allowed supplemental dexamethasone every 1-4 week for up to 6 cycles. Our primary endpoint, sustained response (i.e., platelets ≥ 50 x10(9)/L) at 6 months follow-up, was reached in 58 % of patients in the rituximab + dexamethasone group vs 37 % in the dexamethasone group (p = 0.02). The median follow-up time was 922 days. We found longer time-to-relapse (p = 0.03) and longer time-to-rescue-treatment (p = 0.007) in the rituximab + dexamethasone group than in the dexamethasone group. There was an increased incidence of grade 3-4 adverse events in the rituximab + dexamethasone group (p = 0.04). In conclusion, rituximab + dexamethasone induced higher response rates and longer time-to-relapse than dexamethasone alone. This study is registered at http://clinicaltrials.gov as NCT00909077.