Only a few cases of malignant peripheral nerve sheath tumour (MPNST) associated with Von Recklinghausen's disease or type I neurofibromatosis (NF-1) have so far been reported worldwide, yet the primary disease (NF-I ) does not seem rare even in Africa. We present a case of a 40 year old woman with MPNST of the left thigh associated with NF-1. The diagnosis was based on clinical, radiological and histopathological evidence. She presented with a 25 year history of painless, multiple, generalized skin nodules and hyperpigmented spots. She also noticed a gradually progressive, painless, redundant mass on the left side of the forehead 16 years prior to presentation. Four months before presentation, she noticed another mass at the back of the left thigh, which increased rapidly in size. Examination revealed a middle aged woman with generalized subcutaneous nodules of various sizes (3mm - 2.5cm), multiple café-au-lait spots (2cm-4.5cm), a plexiform neurofibroma on the left side of the forehead measuring 6cm x 5cm x 5cm. There was a firm, non-pulsatile and non-tender mass (11.5cm x 9cm x 5cm) on the posterior aspect of the left upper thigh. The mass was more mobile longitudinally than transversely and was attached to the overlying skin at the summit, the regional Iymph nodes were not enlarged. Most investigations were essentially normal except a plain radiograph, which revealed a soft tissue mass on the left thigh without bony involvement. At surgery, a well localized soft tissue tumour, abutting on the sciatic nerve was widely resected without neural damage to the nerve. Histologic sections of a tru cut as well as the surgical specimens showed a tumour consisting of closely packed serpentine cells arranged in palisades; marked nuclear and cellular pleomorphism and hyperchromatism, many bizarre tumour giant cells, mitotic figures and foci of necroses. The patient received six courses of cytotoxic therapy and is well eleven months after surgery. It is presented to highlight the clinical and pathological features of NF-1 complicated with malignant transformation.