Abstract: Objective To compare the different clinical characteristics of idiopathic hypogonadotropic hypogonadism（IHH） and pituitary stalk interruption syndrome（PSIS）. Methods Clinical characteristics of 74 IHH patients and 36 PSIS patients with normal osphresis admitted to our hospital were retrospectively analyzed. Results Most IHH and PSIS patients were diagnosed as delayed sexual development.Their clinical characteristics were as follows: 1.Most PSIS and IHH patients were delivered in an abnormal fetal position（mainly in a breech presentation）,accounted for 61.1% and 5.4%,respectively（P＜0.01）;2.The body height and the distance between digiti of IHH patients were greater than those of PSIS patients（P＜0.05）.The incidence of IHH and PSIS was higher in the lower part than in the higher part,and the body height was greater than the distance between digiti.However,the distance between digiti was greater than the body height in 75% male IHH patients at the age≥18;3.The development of secondary sexual features was quite slow in both of IHH and PSIS patients;4.Both of IHH and PSIS were complicated with congenital defect or abnormality,especially cryptorchidism;5.The skeletal age was significantly lower in PSIS patients than in IHH patients;6.The PSIS patients were often complicated with deficiency in a variety of anterior pituitary hormones needing replacement therapy,while IHH patients usually were mainly deficient in gonadotropic hormone and growth hormone;7.Pituitary stalk interruption complicated with ectopic posterior was usually found in PSIS patients and reduced pituitary volume was often observed in most IHH patients on MRI images. Conclusion IHH and PSIS patients are usually characterized by delayed development of sexual features.Most IHH patients at the age 18≥years are thin and high,while PSIS patients are short and fat,usually complicated with deficiency in a variety of in pituitary hormones and need replacement therapy.Pituitary MRI is an effective method for the differential diagnosis of IHH and PSIS.