The study consisted of a 2-stage design, which included a dose-ranging phase (during which patients received treatment at their randomized dose) and an expansion phase (after adjustment of dose/regimen to achieve an optimal balance of efficacy and safety). During the dose-ranging phase, patients in each disease group (PV or ET) were randomly assigned in a 1:1:1 ratio independent of each other to receive 1 of 3 treatment regimens with Ruxolitinib, 10 mg twice daily (bid), 25 mg bid, or 50 mg once daily (qd). After patients completed 2 cycles of treatment with Ruxolitinib at the randomized dose, Investigators were permitted to adjust the dose/regimen on an individual basis using their discretion in order to achieve an optimal balance of efficacy and safety. During the expansion phase (ie, after optimization of dose), additional patients with PV or ET were enrolled to receive Ruxolitinib at the dose that was selected upon review of data from the dose-ranging phase. Treatment continued until a patient met a withdrawal criterion, had intolerable toxicity, progression of disease, or withdrew consent.