BACKGROUND Since therapy of rectal carcinoma depends on the extent of disease, staging becomes important. OBJECTIVE To assess the ability of transrectal ultrasonography (TRUS) and computed tomography (CT) to stage rectal carcinoma. METHODS Ten patients with rectal carcinoma were examined by TRUS and plain and contrast-enhanced CT scan; their findings were compared with each other and with those at surgery. RESULTS TRUS identified wall invasion in all ten cases and perirectal fat infiltration in all five cases in whom these were present. Node involvement was detected in five cases on TRUS and two of six cases on CT. Metastasis to bladder (one case) was not recognized by TRUS but was seen on CT. CONCLUSIONS TRUS is inexpensive and superior to CT in staging early rectal carcinoma; limited depth of penetration is its major limitation. CT is useful for the diagnosis of advanced disease.