A case of diffuse-type tenosynovial giant cell tumor arising in the left upper extremity is reported in a 23-year-old man with neurofibromatosis type 1 (NF1)-Noonan syndrome. The predominately mononuclear cellular proliferation with psammomatous calcifications had the immunohistochemical and ultrastructural features of a fibrohistiocytic neoplasm. This uncommon type of soft tissue neoplasm occurring in this unique clinical setting served to open an inquiry into the subject of non-neurogenic tumors in association with NF1 and Noonan syndrome, both manifested in our patient. Nonossifying fibroma of bone as a presumptive fibrohistiocytic tumor is an uncommon but well-documented manifestation in NF1, whereas in Noonan-like syndrome, both giant cell granuloma and pigmented villonodular synovitis are recognized as associated lesions with histologic and immunophenotypic similarities with the diffuse-type tenosynovial giant cell tumor.