The current trend towards limb-sparing surgery in patients with soft tissue sarcomas has increased the need for accurate pre-operative assessment of the primary tumour. Tumour site, extent and relationship to bone and neurovascular structures determine whether adequate radical surgery is feasible or whether more limited excision as a part of multimodality treatment is appropriate. Pre-operative computed tomography (CT) was compared with operative findings in 38 patients with soft tissue sarcomas. CT prediction of muscle group involvement by tumour was correct in 95 per cent and prediction of major artery or vein invasion was correct in 92 per cent and 97 per cent respectively. Assessment of tumour relationship to major peripheral nerve was accurate for thigh sarcomas but was not possible in upper limb tumours. While CT confirmed frank bony involvement in two patients, it failed to distinguish between tumours closely adjacent to periosteum and those with periosteal invasion. Detection of residual or recurrent tumour nodules is less reliable; CT is most accurate before any surgical intervention.