Objectives　To evaluate the relationship between microdeletion or mutation on the Y chromosome and Chinese patients with idiopathic azoospermia and severe oligozoospermia and to establish a molecular detection method.Methods　Microdeletion or mutation detection at the AZFa (sY84 and USP9Y), AZFb, AZFc/DAZ and SRY regions of the Y chromosome. Seventy-three azoospermia and 28 severe oligozoospermia patients were evaluated using PCR and PCR-SSCP techniques.Results　Twelve of 101 patients (12%) with the AZFc/DAZ microdeletion were found, including 8 with azoospermia (11%) and 4 with severe oligozoospermia (14.3%), and 1 patient had a AZFb and AZFc/DAZ double deletion. No deletions in the AZFa or SRY regions were found. No deletions in AZFa, AZFb, AZFc/DAZ or SRY regions were found in 60 normal men who had produced one or more children.Conclusions　Microdeletion on the Y chromosome, especially at its AZFc/DAZ regions, may be a major cause of azoospermia and severe oligozoospermia leading to male infertility in China. It is recommended that patients have genetic counseling and microdeletion detection on the Y chromosome before intracytoplasmic sperm injection.