Malignant peripheral nerve sheath tumour (MPNST) is a relatively rare tumour arisingfrequently in patients with neurofibromatosis, type I (NF1). It is usually a high grade sarcoma. A 65 year old female patient presented with a swelling in left popliteal fossa of two months duration. She had multiple nodular lesions all over the body since childhood. She was subjected to fine needle aspiration for the popliteal mass and was reported as MPNST which was confirmed on histopathology. She developed recurrence within four months time. The prognosis of MPNST is poor. Fine needle aspiration cytology is a very useful, rapid sensitive and inexpensive investigative procedure for the diagnosis of soft tissue tumours and can replace an open biopsy for the diagnosis of MPNST in patients with neurofibromatosis-1.