Introduction. The medical literature contains several definitions of premature ejaculation (PE). The most commonly quoted definition, the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition-Text Revision, and other definitions of PE are all authority based rather than evidence based, and have no support from controlled clinical and/or epidemiological studies. Aim. The aim of this article is to develop a contemporary, evidence-based definition of PE. Methods. In August 2007, the International Society for Sexual Medicine (ISSM) appointed several international experts in PE to an Ad Hoc Committee for the Definition of Premature Ejaculation. The committee met in Amsterdam in October 2007 to evaluate the strengths and weaknesses of current definitions of PE, to critique the evidence in support of the constructs of ejaculatory latency, ejaculatory control, sexual satisfaction, and personal/interpersonal distress, and to propose a new evidence-based definition of PE. Results. The committee unanimously agreed that the constructs that are necessary to define PE are rapidity of ejaculation, perceived self-efficacy and control, and negative personal consequences from PE. The committee proposed that lifelong PE be defined as "... a male sexual dysfunction characterized by ejaculation which always or nearly always occurs prior to or within about one minute of vaginal penetration, and the inability to delay ejaculation on all or nearly all vaginal penetrations, and negative personal consequences, such as distress, bother frustration and/or the avoidance of sexual intimacy." This definition is limited to men with lifelong PE who engage in vaginal intercourse. The panel concluded that there are insufficient published objective data to propose an evidence-based definition of acquired PE. Conclusion. The ISSM definition of lifelong PE represents the first evidence-based definition of PE. This definition will hopefully lead to the development of new tools and Patient Reported Outcome measures for diagnosing and assessing the efficacy of treatment interventions and encourage ongoing research into the true prevalence of this disorder and the efficacy of new pharmacological and psychological treatments.