Objective: To analyze the causes,clinical features and treatment outcomes in patients with nonobstructive azoospermia(NOA)and different severity of hypospermatogenesis(HS).Methods: This is a retrospective study from our reproductive clinic.Data of history,physical findings,serum hormone profiles and genetic studies were collected.The severity of HS was subdivided into three groups(mild,moderate,and severe)based on spermatogenic score.Our goals are to evaluate the causes of HS,clinical features,treatment outcome,sperm retrieval rate(SRR)and factors affecting the SRR among these three groups.Results: The prevalence of HS in our NOA patients is 41.3%(90/218).Twenty-eight(31.1%)patients had at least one prior/current testicular insult,and 12(13.2%)patients had genetic anomalies.Patients with mild HS tended to have higher frequency of testicular insults,whereas patients with severe HS had a significantly higher frequency of genetic anomalies.Removal of testicular insults leads to sperm in ejaculates in four of 17(23.6%)patients.All patients with mild and moderate HS had successful sperm retrieval;however,36 of 41(87.8%)patients with severe HS met with success.No pre-operative parameters were significant predictors of sperm retrieval in our patients.Conclusions: The causes of HS are complex and genetic anomaly is associated with severe HS.Not all patients with severe HS had successful sperm retrieval.Spermatogenesis might be induced in mild HS patients following removal of testicular insults.