The co-existence of a duodenal somatostatin-producing D cell neoplasm and multiple duodenal gastrointestinal stromal tumours (GISTs) in a 61-year-old woman with neurofibromatosis type 1 is reported. Histologically, the D cell neoplasm showed a glandular pattern with psammoma bodies and was metastatic to regional lymph nodes and liver at the time of surgery. Tumour cells were monomorph and showed intense and diffuse immunoreactivity for somatostatin, focal positivity for calcitonin, while were negative for other gastroenteropancreatic hormones including insulin, glucagon, pancreatic polypeptide, serotonin and gastrin. Four submucosal and subserosal GISTs, ranging from 5 to 15 mm in diameter, were composed of uniform spindle-shaped cells lacking mitoses and contained numerous skeinoid fibres. The tumours were positive for CD117, DOG1, vimentin and CD34 and did not have KIT or PDGFRA mutations. The clinical and pathological importance of this unusual association is discussed.