One hundred and thirth-five cases were examined by transrectal ultrasonic probe between January 1984 and December 1986. Of those, 63 were cases of rectal cancer. The ultrasonic shape of rectal cancer was classified into four types on the basis of macroscopic and histologic examination. The depth of invasion of type 1 was pm, and maximum diameter (M-M') was found in the first layer on ultrasonogram. The depth of invasion of types 2 to 4 was a₁ or greater. Maximum diameter of type 2 was found near the first layer, type 4 the fifth layer, and type 3 between the first and fifth layers. The depth of tumor invasion, was determined on ultrasonogram by the condition of bottom echoes. Invasion to pm showed low-grade changes in bottom echoes, while a₁(ss), a₂(s) showed in turn greater changes in bottom echoes. Bottom echoes were also influenced by the stromal structure of the tumor. These results indicated that diagnosis of the depth of invasion should be made with reference to changes in the tottom echoes and stromal structure of the tumor.