OBJECTIVE To evaluate reasons for missed diagnosis of colorectal carcinoma at barium enema (BE) examination and colonoscopy and determine if standards have improved since a similar study in 1981. METHODS Relevant studies obtained within 3 years of diagnosis in 161 patients with colorectal carcinoma treated in 1990 were reviewed. RESULTS Twenty-seven carcinomas were overlooked at BE examination and seven at colonoscopy. Fifteen percent of BE examination errors were purely perceptive (ie, the tumor was visible in retrospect). Another 15% were purely technical. Combined perceptive and technical errors occurred in 45% of cases. Interpretive errors (ie, the lesion was misinterpreted as benign) occurred in 25% of cases. CONCLUSIONS Similar reasons for missing diagnoses of colorectal cancer at BE examination were seen in 1990 and 1981, with a high rate of perceptive errors. Double reading BE studies may reduce this rate, and readiness to perform BE examination after an incomplete colonoscopy may reduce colonoscopic "misses."