To evaluate the prevalence of ultrasound diagnosis of adenomyosis and endometriosis in young women complaining of pelvic pain and to find the symptoms and clinical characteristics associated with these diseases in young women. Cross-sectional study, including 100 young women (14-24 years) with a history of chronic pelvic pain. Women were asked detailed medical hystory and pain symptoms scores (Visual Analogue Scale) and underwent gynecological examination and ultrasound evaluation. The prevalence of endometriosis and adenomyosis in young women amounted to 25.0% and 46.0%, respectively. A significant correlation was found between ovarian endometriosis and adenomyosis. Dysmenorrhea and dyspareunia were risk factors for adenomyosis. Dyschezia, dyspareunia, chronic pelvic pain, presence of sonographic soft markers suggestive of pelvic adhesions, being a worker and having a previous surgery were risk factors for endometriosis. Young women (20-24 years) had a higher incidence of both adenomyosis and endometriosis than adolescents (14-19 years). Our outcomes strengthen the hypothesis of a progressive and common course of the natural history of endometriosis, which initially may manifest with symptoms, then with signs of pelvic adhesions and finally as adenomyosis, ovarian endometriomas or deep infiltrating endometriosis.