Objective: The research is aimed at identifying those risk factors in adolescence which is responsible for diseases in adulthood, and to delineate the endocrinological profile in adolescents with persistent irregular menstrual periods in association with pelvic ultrasound examination. Methods: Our study population included girls who were admitted to the endocrinology and gynecology unit in the Department of Pediatric, L’Aquila, Italy, from March 2016 to January 2017. Our study population included 80 girls, 40 had oligomenorrhea (Group “Olig”) and 40 had no menstrual disorders (Group “Eumen”). At the basal time, we obtained a complete dosage of hormones and investigated metabolic profile. Between the 5th and the 10th day of the spontaneous menstrual cycle we performed a pelvic ultrasound and on the 28th day for the group with “Olig” and on the 14th day for the “Eumen” group, we dosed serum LH and 17-estradiol. Also on the 21st day and on the 35th day, we obtained a dosage of serum progesterone. Results: Pituitary gonadotropins dosages revealed in the periovulatory phase low LH values in the group “Olig”, also associated with lower estradiol values. In addition, luteal phase progesterone showed adequate values only in the “Eumen” group. Moreover, the execution of pelvic ultrasound revealed a statistically significant difference in the endometrial thickness to be associated with estrogenic action not contrasted with progesterone. Conclusions: In our study, we found low LH values in girls with oligomenorrhea with lower estradiol values, which was unable to create positive feedback for the peak of LH. Pelvic ultrasound has highlighted an increased endometrial thickness in presence of persistent menstrual disorders.