Malignant mesenchymoma is a very rare head and neck tumour. To date only 15 cases have been reported in world literature and all in children under 16 years of age. We present here a case of a 40-year-old man with malignant mesenchymoma of the retropharyngeal space. The clinical picture is that of progressive dysphagia, voice change, snoring and dyspnoea. CT scan showed a soft tissue space-occupying lesion of the retropharyngeal space which enhanced very well with intravenous contrast. The tumour was excised in toto and the patient given post-operative radiotherapy. Histopathology showed two unrelated differentiated tissue types (bone and fat) in addition to the fibrosarcomatous element thus satisfying Stout's criteria (Stout, 1948) for a diagnosis of malignant mesenchymoma.