We report on a young female who had presented with fatigue, bilateral knee pain and gait disturbance. Primary hyperparathyroidism was diagnosed together with splenomegaly and anemia. Bone marrow biopsy revealed myelofibrosis. A parathyroid adenoma was excised during surgical intervention. As early as three months after the operation, hematologic parameters improved along with bone markers without any other intervention. The control bone marrow biopsy demonstrated well marked regression in marrow fibrosis. Her spleen has also gradually decreased in size. These findings indicate that her myelofibrosis was the result of primary hyperparathyroidism. Anemia associated with primary hyperparathyroidism may be due to bone marrow fibrosis.