In the last two decades enormous progress has been made in the characterization of premature ejaculation (PE). Although lifelong (primary) PE and acquired (secondary) PE has been known since the 1980s, a new classification of PE has been proposed in 2006 by Waldinger et al., who distinguished two other PE subtypes, e.g., premature-like ejaculatory disfunction and natural variable PE. In 1943, Bernhard Schapiro noted that family members of men with PE often have PE as well. In 1998, Waldinger et al postulated that lifelong PE, and particularly the short intravaginal ejaculation latency time (IELT), may be genetically determined. They postulated that the IELT is distributed according to a continuum, from men who always ejaculate very rapidly to men who always ejaculate after a very long intravaginal ejaculation time. Research in male rats showed this continuum. In two stopwatch studies, such a continuum was also shown in a random sample of men. In 2009, Janssen et al. publish ed a DNA study performed in men with lifelong PE. This study showed that 5-HTT polymorphism was involved in the ejaculation latency time. It appeared that in men with lifelong PE, males with LL genotype had a 100% faster ejaculation time than men with an SS genotype. It is postulated that the IELT is genetically determined by a cluster of genetic polymorphisms of the 5-HTT, 5-HT receptors, 5-HT enzymes and/or polymorphisms of other neurotransmitter systems.