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Background: Myeloproliferative neoplasms, including PMF, PET-MF, and PPV-MF, are a group of clonal stem cell-derived diseases characterized by bone marrow fibrosis, splenomegaly, and debilitating constitutional symptoms. Ruxolitinib (rux), a potent oral JAK1 & 2 inhibitor, demonstrated rapid and durable reductions in splenomegaly and improved MF-related symptoms and quality of life in 2 phase 3 studies (COMFORT-I and -II). Due to unmet medical need, rux has been made available through an individual patient supply program (IPSP) outside the US. Methods: Patients (pts) with PMF, PPV-MF, or PET-MF requiring treatment (as determined by their physician) and classified as high-, intermediate (int)-2-, or int-1-risk with an enlarged spleen were evaluated for eligibility on an individual basis by the sponsor, irrespective of JAK2 mutation status. The starting dose of rux was determined on the basis of baseline platelet count (15 or 20 mg twice daily for pts with platelet counts of 100-200 x 109/L and > 200 x 109/L, respectively) and can be adjusted for efficacy and safety. Dose changes during treatment, adverse events (AEs), and serious AEs (SAEs) are registered throughout the program. Results: To date, 1339 requests have been received from > 800 physicians in 48 countries, including locations in Europe, Latin America, the Middle East, and Asia. The baseline characteristics are shown in the Table for pts whose requests for access were approved (n = 1240). Drug resupply requests are received every {approx} 3 months. Follow-up information, based on the first resupply request, was available for 381/639 (60%) of the pts who were enrolled in the program prior to February 2012; 303 (80%) remain on rux therapy, 37 (10%) have discontinued, 11 (3%) died, and 30 (8%) did not initiate therapy. Spleen response was available for 247 pts (decreased, n = 201; unchanged, n = 39; increased, n = 7). Changes in constitutional symptoms were available for 203 pts (decreased, n = 151; unchanged, n = 49; increased, n = 3). In pts enrolled in the IPSP undergoing rux treatment, most pts who had a decrease in spleen length also had a decrease in symptoms. Dose-modification information was available for 259 pts, of whom 44 had dose increases and 89 had dose decreases. Reasons for dose modifications included efficacy (n = 28), safety (n = 69), and other reasons (n = 36). Safety information was available for 266 pts; 75 reported significant AEs or SAEs as determined by investigators. Enrolled pt characteristics are generally similar to those expected in the overall MF pt population. Thus far, the proportion of pts enrolled in the IPSP with the JAK2 V617F mutation (73%) is higher than that for the general MF population (50%-60%). This may reflect a misconception that JAK inhibition is primarily effective in pts who have the JAK2 V617F mutation, when in fact rux has demonstrated similar efficacy in both pt types in the phase 1/2 251 study and the two phase 3 COMFORT trials. This may also be reflected in the higher proportion of PPV-MF pts in the IPSP than in the general MF population (28% vs 10%-15%), of whom 95% are JAK2 V617 F-positive. Conclusions: Considerable requests for access to rux have been received through the IPSP, highlighting the need for an effective treatment in pts with a range of IPSS risk-assessment scores. The demographics of the IPSP pts are similar to those expected in the overall MF population. Responses and safety patterns observed in the IPSP appear to be comparable to those from the COMFORT trials. (Table presented).