Horseshoe kidney is a difficult sonographic diagnosis, especially if the isthmus is not seen. The purposes of this report are to review the sonographic images in 34 patients with proven horseshoe kidney, to discuss the limitations of ultrasonography in demonstrating the anomaly, and to identify features that would alert the examiner to the possibility of a horseshoe kidney. Among 34 patients, the isthmus was noted in 27. Of the 67 kidneys studied, 52 (78%) were judged to be low-lying, and in 24 (36%) the sonographic images suggested malrotation with anteriorly pointing pelvis. Additional sonographic features seen in the 67 kidneys included a bent or curved configuration of the kidney in the long axis (58%), tapering and elongation of the lower pole (60%), and a poorly defined inferior border of the kidney (84%). These features should suggest the presence of a horseshoe kidney and direct the examiner to search for the isthmus.