The case of a young boy with primary hyperparathyroidism due to an adenoma is reported. The tumor was localized by ultrasonography, and a close correlation between the image and the surgical findings was found. Since primary hyperparathyroidism in children under 15 years of age is frequently due to adenomata larger than 1.5 cm it is suggested that ultrasonography of the neck should be included in the work-up of every children suspected to have this pathology.