Carcinosarcoma is a rare tumour of the salivary gland. The ultrasound and CT appearances of a rapidly enlarging carcinosarcoma in the parotid are described. Both modalities revealed a 4-cm tumour with relatively benign features and no evidence of lymphadenopathy. Ultrasound showed a well-defined mass of homogeneous low echogenicity and posterior acoustic enhancement. Computed tomography showed a parotid mass of homogeneous attenuation similar to muscle, and homogeneous enhancement following contrast. The clue to the malignant nature of the lesion was a short indistinct superficial margin with tumour extension into the adjacent subcutaneous tissues.