A 31-year-old woman, whose chief complaint was back pain, was found to have an echocardiographic abnormality suggestive of a left atrial myxoma. Angiography clearly showed a large radiolucent mass protruding from the left atrium into the left ventricle during diastole. X-rays of the sacrum disclosed the presence of a malignant tumour. Biopsy specimens taken from the tumour in the sacral plexus showed a malignant neurilemmoma. Despite extensive chemotherapy, widespread metastases developed and the patient died four months after admission. Necropsy disclosed three discrete tumours in the left atrium, which were found to be malignant neurilemmoma, shown on histology to be metastases from the primary in the sacral plexus.