The objective is to evaluate the appearance of phleboliths and distal ureteral stones by determining their roundness and presence of central lucency on thin-slice CT. Seventy-seven patients with pelvic radioopacities at unenhanced CT were selected. Those patients consequently underwent thin-slice CT with 1-mm collimation, a FOV of 10 cm, a pitch of 1:1 and a bone reconstruction algorithm. Three radiologists reviewed all images for roundness and the presence of central radiolucency. No calculi showed central lucency on either imaging technique used. Thin-slice CT revealed central lucency in 60% of phleboliths with 100% specificity. Three of 40 ureteral stones showed round contour. Thin-slice CT revealed a round contour in 97% of phleboliths with 93% specificity. Central lucency is a characteristic finding of pelvic phleboliths on thin-slice CT. This finding can therefore be used in combination with roundness as a problem-solving tool in differentiating phleboliths from distal ureteral stones.