© 2021 John Wiley & Sons LtdWhat is known and objective: Primary myelofibrosis (PMF) is characterized by myeloid cell proliferation and prominent bone marrow fibrosis. Ruxolitinib, a selective inhibitor of JAK 1 and 2, significantly reduces constitutional symptoms and spleen size compared with placebo, and has significant clinical benefits in patients with myelofibrosis. The most common haematological side effects are thrombocytopenia and anaemia, and the most common non-haematological side effects are grade 1–2 diarrhoea and pyrexia. Leukocytoclastic vasculitis is small vessel vasculitis, characterized histopathologically by immune complex-mediated vasculitis of the dermal capillaries and venules in the lower extremities, which can be seen as palpable purpura. Although the cause is 50% idiopathic, the aetiology of leukocytoclastic vasculitis can be collected under many headings. Case Summary: The case is here presented of a patient with PMF who developed leukocytoclastic vasculitis after ruxolitinib treatment. Ruxolitinib was discontinued as the lesions were thought to be drug-related and all skin lesions disappeared approximately 2 months after termination of the drug. When the ruxolitinib treatment was restarted at the same dose (2 × 15 mg), the skin lesions recurred. The drug dose was reduced to 1 × 15 mg, and the rashes disappeared. Currently, the patient has no active complaints and is being followed up with ruxolitinib 1 × 15 mg without any complications. What is new and Conclusion: To the best of our knowledge, leukocytoclastic vasculitis due to ruxolitinib is extremely uncommon. This case report can be considered to contribute to the literature of this rare event.