Based on clinical observations, the “encased spleen” syndrome, a nosologic entity, is described. It comprises a painful abdominal condition caused by dense adhesions (synechia) between the greater omentum, the spleen, the undersurface of the diaphragm, and the adjoining posterolateral abdominal wall in patients with no previous history of surgery, peritonitis, or other abdominal trauma. The central pathological finding is fibrosis of the spleen, due most probably to repeated small infarctions of the organ. Treatment is discussed in light of the eight cases studied. Splenectomy associated with subtotal omentectomy rid the patients of the pain.