Primary autoimmune myelofibrosis is a very rare condition characterized by peripheral blood cytopenias, bone marrow fibrosis with lymphoid aggregates, and by the finding of autoantibodies in peripheral blood, suggesting a systemic autoimmune process. Patients can be frequently misdiagnosed as having the more common disorder primary myelofibrosis, a myeloproliferative neoplasm. We report the case of a patient with primary autoimmune myelofibrosis with emphasis on the clinical and pathological features that lead to the diagnosis.