To compare intraluminal ultrasonographic (ILUS) findings with histological findings of rectal carcinoid tumors, 35 patients with rectal carcinoid tumors were reviewed. The results were as follows: 1) The rectal wall was visualized as a seven- or nine-layer structure by means of ILUS in 81% of the patients. 2) The possibility that the thin hyperechoic third layer above the tumor on ILUS corresponds to the muscularis mucosae and fibrointerstitium above the tumor histologically. 3) In cases with relatively high internal echoes, the amount of fibrointerstitium exceeded that of tumor cells histologically. 4) In cases with nonuniform internal echo patterns, tumor cells were separated by thick fibrointerstitium forming nodular nests.