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Introduction and importance Histiocytic sarcoma (HS) is a rare, aggressive malignant neoplasm of hematopoietic cell origin. Primary HS of the proximal humerus, without involvement of lymph nodes or bone marrow, or systemic features, is very rare. Case presentation We report a rare case of primary bony HS of the proximal humerus without bone marrow involvement in a healthy 33-year-old pregnant woman. She was successfully treated with surgical resection during pregnancy and radiotherapy post-delivery. Clinical discussion This is the first report of a patient with primary bony HS during pregnancy. This highlights the fact that although HS is a neoplasm of hemolymphoid cell lineage, it frequently arises in non-lymphoid organs. Conclusion This case emphasizes the importance of a multidisciplinary approach and the need for balancing treatment risk in a patient with primary bone HS during pregnancy., Highlights • Histiocytic sarcoma is a rare aggressive malignant neoplasm of hematopoietic cell origin. • Primary bony histiocytic sarcoma during pregnancy is extremely rare and difficult to diagnose. • Treatment is challenging in a patient with histiocytic sarcoma during pregnancy.