Histiocytoses are rare disorders and most orthopedic surgeons are unfamiliar with this diagnosis. We report a case of synovial non-Langerhans cell histiocytosis (LCH) located in the shoulder, which has not been reported in the literature previously.A 24-year-old female patient presented to our clinic with shoulder pain and decreased range of motion. MRI results suggested pigmented villonodular synovitis. Arthroscopic synovial debridement and biopsy were performed. Histologic examination came back as non-LCH of the shoulder. Hematology/oncology evaluation indicated localized disease and no further treatment was necessary. At the 6th month follow-up, the patient gained full shoulder motion and is symptom free.This case represents a rare diagnosis of synovial non-LCH which should be considered in the differential diagnosis of synovial diseases. A misdiagnosis could result in inadequate treatment, and coordination with the hematology/oncology department is of utmost importance in the treatment of this neoplastic disease.