The study group was formed by adolescent men 13.5–17 years old with delayed puberty: 56 for the purpose of development a method of differential diagnosis, 30 for its control (control group).  Anamnesis, stage of puberty, testicular volume were assessed; serum levels of LH, FSH, testosterone (T) were determined by chemiluminescent analysis and inhibin B, AMH by ELISA. Stimulation tests were performed with triptorelin and human chorionic gonadotropin (3 days). Patients were followed up for 6–24 months. We`ve created a method that allows differentiate HH and CDP. Through the ROC-analysis the most sensitive and specific HH markers were identified. The basal levels of LH, FSH, T, and inhibin B were selected as most available for outpatient testing. Based on the results of our own research and scientific data we selected ranges of values and rated LH, FSH, T and inhibin B depending on them (marks). Then we assigned the coefficients (k) for each hormone. Scores were calculated by multiplying the marks by k then summed and normalized to the maximum amount the patient could get. To increase the accuracy of diagnosis an age coefficient was introduced. The result of the calculation was the result of the scoring (S). S for CDP (10.65 [3.13-14.91]) differed significantly from that for HH (76.46 [57.79-83.74]) (p<0.001). Diagnoses based on S (<21.16 and ≥55.07) in the control group were confirmed by follow up data in 97% cases. An algorithm for the differential diagnosis of HH and CDP by using S has been developed. The result of scoring of LH, FSH, testosterone, inhibin B levels ≥55.07 makes it possible to diagnose hypogonadotropic hypogonadism, <21.16 – constitutional delay of puberty with a high probability. In case of score ≥21.16 but <55.07, calculation of the inhibin B/AMH ratio and/or stimulation tests are required.