Eight primary leiomyosarcomas of bone were registered in the files of the Basel Bone Tumor Reference Center, Basel, Switzerland, for the period 1972 to 1990. The mean age of the patients (six males and two females) was 43.7 years (range, 11 to 87 years). The tumors were located in the long bones, the fingers, and the clavicle, and presented radiologically mainly as slightly to moderately aggressive lesions (grades IB to II according to Lodwick). They reacted immunohistochemically with antibodies against alpha-smooth muscle actin (alpha-SMA), and total muscle actins (eight of eight), vimentin (seven of eight), desmin (three of eight), keratin (four of eight), type IV collagen (six of eight), laminin (five of eight), and S-100 (one of eight). Seven patients underwent surgery (five, resection; two, amputation). Some of them had received preoperative or adjuvant chemotherapy or radiation therapy. One patient with a metastasized tumor had received chemotherapy only. Tumor recurrences were observed in two cases. Four patients developed metastases of whom two were treated with chemotherapy or tumor resection. During a follow-up period of 1 to 72 months (mean, 46.5 months) four of the eight patients survived for up to 72 months, among them the only patient with grade 3 tumor and treated metastases.