Several empirical treatments have been proposed to treat idiopathic infertility in men, including follicle-stimulating hormone (FSH). FSH administration is effective in patients with hypogonadotropic hypogonadism, which suggests it might be useful in patients with oligozoospermia who have normal FSH levels. Indeed, many studies have evaluated the efficacy of FSH administration in these patients, several of which have shown improvements in sperm parameters. By contrast, other studies have not reported any significant effect of FSH administration on conventional sperm parameters, although some of have reported the normalization of spermatozoon ultrastructural morphology, as well as reductions in DNA fragmentation, production of reactive oxygen species and aneuploidy. Contemporary studies suggest that the response to FSH treatment in oligozoospermic patients might, at least partially, reflect polymorphisms of the FSH receptor gene. Thus, FSH administration in oligozoospermic men with normal serum FSH levels might be efficacious only in selected patients. For this reason, additional studies are needed to determine the predictive factors and clinical conditions that can be used to identify patients who could benefit from FSH treatment.