DAX-1 [dosage-sensitive sex reversal-adrenal hypoplasia congenital (AHC) critical region on the X chromosome gene 1; NR0B1] is an orphan nuclear receptor that acts as a transcriptional repressor in adrenal/gonadal development, steroidogenesis and probably spermatogenesis. An alternatively spliced form called DAX-1A (NR0B1A) has been described in several tissues including the testis, and in vitro studies have shown an inhibitory effect on DAX-1 transcriptional function. We aimed to study the mRNA and protein expression of DAX-1 in testicular tissues of 65 men with primary spermatogenic failure [complete Sertoli cell only syndrome (SCOS), focal SCOS, maturation arrest and mixed atrophy] compared with 33 controls with normal spermatogenesis. As a novel finding, we observed intense immunostaining, not only in the nucleus of Sertoli cells, but also in pachytene spermatocytes and round spermatids. The quantitative mRNA expression of DAX-1 and DAX-1A was similar between cases and controls and was not associated with the levels of gonadotrophins and steroids. Moreover, DAX-I transcript expression level was ∼750-fold higher than DAX-1A, and there was a strong positive correlation between them (r = 0.52; P< 0.001). We conclude that, in addition to Sertoli cells, DAX-1/DAX-1A is expressed in germ cells from spermatogonia to round spermatids. Besides, the similar mRNA expression of DAX-I and DAX-IA in testicular tissues from cases and controls does not support the involvement of DAX-1 in the etiology of primary spermatogenic failure. Finally, the low level of expression of the alternative transcriptional variant DAX-1A would not support its putative inhibitory function in vivo.