OBJECTIVE. Our objective was to compare the value of endoluminal sonography with the value of helical CT in the preoperative assessment of crossing vessels in patients with ureteropelvic junction (UPJ) obstruction. SUBJECTS AND METHODS. Thirteen patients with UPJ obstruction underwent contrast-enhanced helical CT with multiplanar reformations and endoluminal sonography. Imaging preceded surgery for UPJ repair. On imaging, vessels were considered significant if greater than or equal to 2 mm in diameter and within 1 cm of the UPJ. RESULTS. Three patients had no crossing vessels revealed by either study. On sonography, another patient had a vessel revealed with a diameter that varied between 1.3 and 2.2 mm: on CT no correlate was detected. The remaining nine patients had vessels revealed by both techniques. On CT, four patients had two vessels revealed find five patients had single vessels revealed for a total of 13 vessels revealed by CT. On sonography, five patients had two vessels revealed and five patients had single vessels revealed. Thus, 15 vessels were revealed by sonography. Both arteries and veins were revealed anterior, posterior, anti medial to the UPJ; no lateral vessels were seen. Four patients underwent laparoscopy, during which the absence, presence, and location of vessels were found to correlate with sonography and helical CT. CONCLUSION. Endoluminal sonography and helical CT were similar in revealing crossing vessels in patients with UPJ obstruction.