Lifelong premature ejaculation is characterized by early ejaculations occurring at nearly every intercourse, with nearly every female partner, and most often from the first sexual encounters in puberty and adolescence. Premature ejaculation has always been regarded as a psychological disorder that had to be treated by psychotherapy. However, there is no evidence supporting general psychological causes and efficacy of behavioural treatment for this male sexual complaint. In contrast, there is increasing evidence for the efficacy of daily treatment with some selective serotonin reuptake inhibitors (SSRIs) and on-demand treatment with clomipramine and anesthetic ointments. Data of recent epidemiological stopwatch research of the intravaginal ejaculation latency time (IELT) support an ejaculation distribution theory, of a continuum of IELT in the general male population. Using the 0.5 and 2.5 percentile as accepted standards of disease definition, lifelong premature ejaculation has been defined as a neurobiological dysfunction with an unacceptable increase of risk to develop sexual and psychological problems at any time during a lifetime. It is proposed that all men with an IELT of less than 1minute have “definite” premature ejaculation, while men with IELTs between 1 and 1.5minutes have “probable” premature ejaculation. In addition, it is proposed to define the severity of premature ejaculation (none, mild, moderate, severe) in terms of associated psychological problems.