OBJECTIVE Experienced surgeons have the highest sensitivity in the localization of parathyroid adenomas in patients with primary hyperparathyroidism. Correct preoperative localization, however, allows unilateral neck exploration with subsequently reduced operative time and complication rate. In this prospective study, we investigated the accuracy of preoperative high-resolution ultrasound in combination with colour-Doppler sonography for the detection of parathyroid lesions. METHODS Ninety-eight patients (mean age 59.1 years, range 15-86) who referred to our department with symptomatic primary hyperparathyroidism were included in the study from January 1998 to June 2002. Sonography was performed by experienced examiners. The exact diagnosis was based on surgical findings and histology in all patients. RESULTS The overall sensitivity for the sonographical localization of the adenomas on the correct side of the neck was 86 %. Twenty-three percent of the adenomas located on the cranial margin of the thyroid gland were diagnosed correctly, as were 92 % of the lesions located caudally (p = 0.0001). The detection of feeding vessels was possible by colour-Doppler sonography in 60 % of the cases. The diagnosis was correct for 93 % of these suspected adenomas. No vessels were detected in the remaining lesions, and only 39 % of these tumours were diagnosed correctly (p = 0.0001). CONCLUSIONS High-resolution ultrasonography by experienced examiners is a highly sensitive procedure for the preoperative diagnosis of parathyroid adenomas in patients with primary hyperparathyroidism. With this method, a unilateral neck exploration is sufficient in about 90 % of the patients. Additionally, detection of feeding vessels by colour-Doppler sonography is an important indication of a parathyroid lesion. Nonetheless, the experienced surgeon remains the standard of reference.