PURPOSE: Controversy exists as to whether sartorius muscle is completely invested in fascia. If it is, then direct tumour involvement from soft tissue sarcoma of the anterior thigh would be unlikely and would justify omitting sartorius from the radiotherapy volume. SUBJECTS AND METHODS: Eight thighs in six cadavers were examined in the dissecting room. Using a previous case, conformal radiotherapy plans were prepared to treat the anterior compartment of the thigh including and excluding sartorius. The corridor of unirradiated normal tissue was outlined separately. RESULTS: In all cases, sartorius was enclosed within a fascial sheath of its own. In four of the six cadavers, there was clear evidence of a fascial envelope surrounding sartorius, fused to the fascia lata and medial intermuscular septum. In two, sartorius was fully ensheathed in the upper half of the thigh; in the lower half the intermuscular septum became thin, and blended with the tendinous aponeurosis on the surface of vastus medialis in an example case. By excluding sartorius, the volume of the anterior compartment was reduced by 8%, but the volume of the unirradiated normal tissue corridor increased by 134%. With sartorius included, the unirradiated corridor became very small inferiorly, only 6% of the circumference of the whole leg, compared to 27% with sartorius excluded. DISCUSSION: The anatomy suggests that sartorius could be safely omitted from the clinical target volume of anterior compartment soft tissue sarcomas. This substantially increases the size of the unirradiated normal tissue corridor, expressed as a volume and a circumference, which could give a clinical advantage by reducing normal tissue complications.