The concept that an elevation of testicular temperature results in impairment of spermatogenesis is widely accepted. Here, current knowledge concerning genital heat stress and its consequences in men is reviewed. Duration of sitting during work positively correlates with daytime scrotal temperatures and daytime scrotal temperature negatively correlates with semen quality. However, the assumed negative correlation between duration of sitting and semen quality could not be shown in the available studies. Fertility parameters of professional drivers with long periods of sitting in vehicles were impaired; however, for predominantly affected drivers of vans, trucks or industrial heavy machinery potential confounders have to be considered. Wearing tight fitting compared with loose-fitting underwear is associated with significantly higher scrotal temperatures. However, available observations suggesting a link between tight-fitting underwear or trousers and impaired semen quality are not convincing. Studies addressing professional exposure to high temperatures delivered conflicting results concerning fertility parameters. The postulated negative impact of sauna visits on semen quality is not sufficiently underlined by the available studies. Oligozoospermic men with a varicocele have significantly higher scrotal temperatures than normozoospermic men, and according to several studies varicocelectomy normalises scrotal temperatures. A further link has been reported between fever and deteriorated semen quality. Contraception via genital heat stress has been demonstrated using hot sitting baths or insulating suspensors. However, down-regulation of spermatogenesis is inconsistent and unsafe. On the other hand, scrotal and consecutively testicular cooling is able to improve semen quality.