To establish the incidence and causes of unintentional weight loss and to compare prognoses. Prospective. Secondary referral centre. 158 patients (89 female, 56%; 69 male, 44%) referred by general physicians for unexplained weight loss or for other reasons. In the latter case, weight loss was established after admission to hospital. Follow-up lasted for up to 3 years. Determining the course of weight loss in patients with diagnosed and undiagnosed causes. The cause of weight loss was established in 132 (84%) patients and remained unclear in 26 (16%). Reasons were non-malignant (60% of patients) and malignant (24%) diseases. Psychological disorders represented 11% of the non-malignant group. A gastrointestinal disease caused weight loss in 50 (30%) patients. Of malignant disorders, 53% (20 of 38 patients) were gastrointestinal. Amongst the non-malignant group, 39% (30 of 77 patients) had somatic disorders. The prognosis for unknown causes of weight loss was the same as for non-malignant causes. Contrary to common belief, weight loss is not usually due to a malignant disease. A gastrointestinal tract disorder accounts for weight loss in every third patient. If minimal diagnostic procedures cannot establish a diagnosis, then endoscopic investigation of the upper and lower gastrointestinal tract and function tests should be performed to exclude malabsorption.
