A 45 year old male patient was referred to hospital after syncope during defaecation. Rapid peranal blood loss occurred shortly after admission. Gastroscopy and coloscopy performed as first line diagnostic measures failed to detect the source of haemorrhage. Ultrasound (US) revealed a hypoechoic and hypervascularized tumor mass in the right lower abdomen. A gastrointestinal stromal tumor (GIST) of the jejunum was diagnosed after laparatomy. Collectively US should be among the first line diagnostic procedures in younger patients presenting with lower gastrointestinal haemorrhage.