Background: The aim of the paper was the US evaluation of hormonal disorders and treatment results in adolescent girls and boys with breast cysts. Material/Methods: In the years 2001–2009, US examination of the breast was performed in 427 children aged 10–18 years, with clinically suspected breast pathologies. The indications for US examination typically included pain, breast swelling and a palpable tumor. The US examination was performed using a 7–12 MHz linear transducer. Results: Breast cysts were found in 42 children: 36 adolescent girls and 6 boys with gynecomastia. Infected cysts were found in 35 children. The cysts ranged in size from 5 mm to 30 mm. In 5 of the girls, large cysts were treated by an incision and drainage, and in all the children with infected cysts, antibiotic therapy was used. Hormonal disorders were found in 30 girls. A follow-up examination was performed, and the observation time varied from 1/12 to 2 years. The cysts disappeared completely in 30 children. Hormonal therapy was introduced in 5 girls. Conclusions: Breast cysts found in US examinations are indications for check-up examinations including endocrinological diagnostics and, if the cyst is persistent, possibly for hormonal treatment.