Deletions in distal Yq interval 6 represent the cause of 10-15% of idiopathic severe male infertility and map to a region defined AZFc (azoospermia factor c). The testis-specific gene DAZ is considered a major AZFc candidate, and its deletion has been associated with a severe disruption in spermatogenesis. However, DAZ is actually a multicopy gene family consisting of seven clustered copies spanning about 1 megabase. Only deletions removing the entire DAZ gene cluster together with other genes have been reported in infertile males. Because no case of spermatogenic failure has been traced to intragenic deletions, point mutations, or even deletions not involving all the DAZ copies, the definitive proof for a requirement of DAZ for spermatogenesis is still debatable. Here we report the first case of a partial deletion of the DAZ cluster removing all but one of the copies. This deletion is present in a patient affected with severe oligozoospermia who had a testicular phenotype characterized by a great quantitative reduction of germ cells (severe hypospermatogenesis). The absence of this deletion in the fertile brother of the patient suggests that this de novo mutation indeed caused the spermatogenic failure.