Thirty-nine patients with pathologically proved renal cell carcinomas 3 cm or les in diameter were examined. Results of intravenous urography (n = 30) were true positive in 20 patients and false negative in ten (sensitivity, 67%). Renal ultrasound (US) (n = 29) had true-positive results in 23 patients and false-negative results in six (sensitivity, 79%); computed tomography (CT) (n = 36) had true-positive results in 34 and false-negative results in two (sensitivity, 94%). For selective renal angiography (n = 35%), the results were true positive in 26 and false negative in nine (sensitivity, 74%), with typical hypervascular renal cell carcinomas demonstrated in 17. Finally, the findings of percutaneous fine-needle aspiration biopsy were true positive in one of five patients when US guidance was used (sensitivity, 20%) and in five of eight when CT guidance was used (sensitivity, 62%). Small renal cell carcinomas are more frequently encountered in clinical practice than heretofore realized, and they are best imaged by CT.