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Fibrodysplasia ossificans progressive (FOP) is an ultra-rare genetic disorder that is caused by a mutation in the ACVR1 gene and provokes severe heterotopic ossification. Since flares of the disease are associated with inflammation, it is assumed that JAK inhibitors can control active FOP due to blocking multiple signaling pathways. Aim of Study: To assess the safety and efficacy of tofacitinib in patients with FOP refractory to standard of care treatment. Material and Methods: In the retrospective observation study we included information about 13 genetically confirmed FOP patients who were treated with tofacitinib 5 mg twice a day. All patients initially failed treatment with NSAIDs, corticosteroids, and bisphosphonates. We evaluated the patients 12 months before the beginning of their treatment with tofacitinib and continued evaluating to at least 12 months of their tofacitinib treatment period. Results: In 7 boys (54%) and six girls (46%) tofacitinib was prescribed at the age of 10.2 (ranged 2.2–19.6) years. Onset age was 1.5 (ranged 0.1-6.0) years. Main clinical features were malformed great toes (n = 13; 100%), short malformed thumbs (n = 9; 69%), peripheral osteochondromas (n = 9; 69%), abnormalities of the cervical spine (n = 13; 100%), multiple heterotopic ossifications (n = 13; 100%). The mean diagnostics delay was 44 (range: 1; 165) months. During the trial, the median (25%; 75%) frequency of flares decreased from 10 (6; 12) during 12 months before the baseline to 0 (0; 2) in the following 12 months and 0 (0; 0) in 24 months of treatment. There were no deteriorations of the CAJIS index during the study, except for only one patient whose CAJIS index deteriorated by 1 point. Improvement in the range of motion in the large joints was noted in 31% of patients. NSAID, oral and intravenous corticosteroids were successfully decreased from 100%; 61.5%, and 15.4% (baseline) to 46.2%, 7.7%, and 0% (12 months) and 22.2%, 0%, and 0% (24 months), consequently. The drug tolerance was good. No severe adverse events were registered. Conclusion: Tofacitinib is a highly efficient, well-tolerated option that may prevent FOP flares. Further studies of the therapeutic potential of JAK-kinase inhibitors in FOP patients are needed. [ABSTRACT FROM AUTHOR]