Y-chromosomal microdeletions, associated with oligozoospermia or azoospermia, are usually de novo deletions in the affected patients. We report here the rare case of an affected father who transmitted a Y-chromosomal microdeletion to at least two of his three sons naturally and who also fathered a daughter. The extent of the deletion, which was determined with new STS-primers and covers 3.5 Mb, was identical in the father and his azoospermic sons. To determine any possibly modifying influence of other genes involved in spermatogenesis, we analysed two polymorphisms of the DAZL gene, the autosomal homologue of the deleted DAZ gene. DAZL and DAZ might be functionally related to each other. However, we found identical polymorphisms in exon 2 and 3 of the DAZL gene, in both father and his sons, corresponding to the most prevalent genotype in fertile men. Thus, other genes or environmental factors must modify spermatogenesis in men with identical Y-chromosomal microdeletions.