[Show abstract][Hide abstract] ABSTRACT: Teratozoospermia and its significance for male fertility problems is discussed. Different points of view and available information concerning the phenomenon of teratozoospermia have been presented. Ongoing debate about the influence of sperm morphology on male infertility and IVF results emphasizes the fact that when sperm morphology is evaluated using strict criteria, this parameter is thought to have an excellent predictive value and shows a significant positive correlation with successful fertilization. Selective abilities of zona pellucida to differentiate between morphologically normal and abnormal spermatozoa, the superior role of acrosomal morphology assessment in the prediction of IVF outcome, and the involvement of cell surface molecules in the adhesion of spermatozoa to oocytes are described. The usefulness of the hamster oocyte penetration assay (HOPA), which is important not only because of its predictive value of sperm function, but also because of its role as a tool for visualizing sperm chromosomes, was found to be questionable in cases of teratozoospermia. Cytogenetic findings related to teratozoospermia are controversial as classical methodology of visualizing sperm chromosomes (through HOPA) may cause selection of sperm metaphases which can be obtained only from good-penetrating spermatozoa. There are few reports presenting chromosome complements of abnormal sperm visualized with the help of micromanipulation. There is clear evidence that a variety of genetic defects can affect spermatogenesis. The possible genetic background of teratozoospermia is discussed.