Peripheral primitive neuroectodermal tumours (pPNETs) are highly malignant, small-cell neoplasms found mainly in children and young adults. Recent advances in immunohistochemistry and genetic typing have led to reports of a close relationship between pPNET and the previously difficult-to-classify Ewing's sarcoma. We report a case of pPNET involving the left maxillary sinus in a 23-year-old female who presented with a 2-month history of unilateral left-sided nasal obstruction, rhinorrhoea and recurrent bloody nasal discharge. A CT scan of the paranasal sinuses showed a large mass (10 x 7 x 3 cm3) arising from the left maxillary sinus, with signs of bone destruction and invasion of the left orbital floor and pterygomaxillary fossa. MRI revealed a heterogeneous hyperintense signal on a T2-weighted image in the left maxillary sinus. The tumour was surgically removed by means of external lateral rhinotomy. Pathological examination showed a sheet of small cells with irregular nuclei. Immunohistochemical studies demonstrated positive immunoreactivity for neurone-specific enolase, synaptophysin, chromogranin, vimentin, S-100 protein and p30-32 MIC-2 gene product. The patient was treated with chemotherapy consisting of cyclophosphamide, vincristine, adriamycin and actinomycin D, together with radiotherapy to a total tumour dose of 60 Gy. After 59 months of follow-up, the patient remained free of disease and a repeat MRI scan was normalized, with no sign of residual tumour.