Until recently, the presence of occult ganglions could be determined only by surgical exploration. This prospective study investigated the reliability of ultrasound in the diagnosis of occult ganglions in a patient series over 4 years. The sensitivity, specificity, and accuracy of ultrasound, as well as its positive and negative predictive values, were determined in 83 patients suspected of having an occult wrist ganglion and who had persistent pain and consented to an operation. Examinations were carried out with a 7.5-MHz linear probe and spacer. Outcome of surgery and histologic examination served as the gold standard in 168 patients who had undergone ultrasound; 89 underwent surgery. In 83 patients for whom enough information was available to allow statistical assessment, sensitivity, specificity, and accuracy rates of 88%, 85%, and 87% were respectively obtained. In dorsal wrist ganglions (75%), better results were obtained: a sensitivity rate of 93%, a specificity rate of 86%, and an accuracy rate of 91%. It was concluded that ultrasound of the wrist can be used as a first-line imaging procedure in clinically inconclusive situations and that ultrasound evidence of an occult dorsal ganglion is a reliable indicator for surgery.