During the period from April 1973 to June 1975, 31 cases of palpable mass on the right lower abdomen in adult have been observed at Korean General Hospital for determining basic type of mass, site of origin, age incidence, signs and symptoms of the patients as well as radiological findings. The results obtained are as follows: 1. The disease is more common in males than females, with 1.8:1 ratio. Peak age incidence of palpable mass on the right lower abdomen is 4-5th decades. 2. The most frequent complaint of palpable mass is localized abdominal pain, melena and generalized abdominal pain are next frequent symtoms. Most of the patients with malignant tumor in the right colon and terminal ileum complained melena. 3. Thirteen cases (42%) of palpable mass on the right lower abdomen are developed in less than 15 days, and adenocarcinoma was most commonest histological finding in the right colon. 4. The commonest location of palpable mass on the right lower abdomen occurs in the ce um and acending colon. 5. Barium enema examination was the most signific-ant and useful study in the roentgenological evaluation of right lower abdominal mass in adult. 6. The commonest lesion of palpable mass on the right lower abdomen was adenocarcinoma of the right colon, the next common lesions were right ovarian cyst and periappendiceal abscess. 7. A case of ectopic seminoma in the terminal ileum was encountered.