We report on a case of a 36-year-old lady who presented with large, painful soft-tissue swellings of both Achilles tendons. MRI demonstrated fusiform enlargement involving the Achilles tendons bilaterally. The tendons returned heterogeneous signal intensity characterised by a diffuse reticulated appearance. The right tendon mass was treated with a wide marginal excision and Achilles tendon reconstruction. The histology confirmed Achilles tendon xanthoma. Further metabolic investigation revealed the patient to have a rare autosomal recessive condition called cerebrotendinous xanthomatosis (CTX). Her brother was also affected. CTX is easily treatable if diagnosed early, and should be suspected in patients presenting with bilateral Achilles tendon xanthomas and normal plasma lipid levels.