Introduction. This is the case of a young male patient who presented to his 
family physician with atypical left foot pain, which was extremely resistant to 
analgesia and caused significant disability. Despite extensive investigations, 
the cause of his pain was not identified until 18 months after his initial 
symptoms, when the official diagnosis of malignant peripheral nerve sheath 
tumour (MPNST) was made. Detailed review of the patient's past history 
established the diagnosis of type I neurofibromatosis (NF-1), previously 
undetected. Discussion. NF-1 is an autosomal dominant genetic disorder caused by 
loss of function mutations of the NF1 gene in chromosome 17. Patients with this 
condition are at increased risk for developing MPNSTs which, however, are 
treatable only in early stages. Conclusion. Although monitoring NF-1 patients 
for the development of MPNSTs is common practice, the index of clinical 
suspicion in patients without an established NF-1 diagnosis is low. Any atypical 
pain in young adults should raise the possibility of this malignancy, and this 
case illustrates the fact that MPNSTs can be the first manifestation of NF-1 in 
patients previously undiagnosed with the disease.