We describe a case in which segmental resection of the third and fourth portion of the duodenum was performed for a very rare duodenal gastrointestinal tumor (GIST). A 58-year old man presented with melena. Capsule endoscopy revealed a pathological bleeding of the duodenum and oral contrast-CT enema confirmed a lesion of the duodenum inferior knee, measuring 3.5 cm in diameter. Such an image suggested a duodenal leiomyoma. Segmental resection of the third and fourth portion of the duodenum after intestinal derotation (Valdoni-Strong's procedure) was carried out and there were no post-operative complications. Pancreas sparing duodenal resection is at the present time indicated only in selected cases. The duodenal resection associated with bowel and right colon derotation has proved to be a safe and adequate procedure and could be preferred to other procedures.