Introduction.  Large, well‐designed observational or clinical efficacy and safety randomized clinical trials are required to identify the prevalence of premature ejaculation (PE) and its associated risk factors, to characterize the dimensions of PE and the basis for treatment‐seeking behaviour, and to achieve regulatory approval of new drug treatments. Aims.  The objective of this article was to make recommendations for the criteria for defining and selecting the study population. Main Outcome Measures.  Contemporary published data on clinical trial design and the epidemiology, definitions, dimensions, and psychological impact of PE. Methods.  Contemporary data on the epidemiology, definitions, dimensions, and psychological impact of PE were reviewed, critiqued using the principles of evidence‐based medicine, and incorporated into a series of evidence‐based recommendations for standardization of patient selection for clinical trials in PE. Results.  Data from PE observational, interventional, and treatment preference studies are only reliable, interpretable, and capable of being generalized to patients with PE when study populations are defined by the constructs of an ejaculatory latency time of less than about 1 minute on all or nearly all occasions, the inability to delay ejaculation, and the presence of negative personal consequences, such as distress, bother, frustration, and/or the avoidance of sexual intimacy. Conclusion.  These constructs can be incorporated into a multidimensional evidence‐based definition of PE and/or single‐item questions or multi‐item diagnostic questionnaires. The International Society of Sexual Medicine definition of PE reflects the contemporary understanding of PE, represents the state‐of‐the‐art multidimensional definition of PE, and is recommended as the basis of diagnosis of PE for all PE clinical trials. McMahon CG. Interventional and treatment preference studies—Part I—Defining and selecting the study population. J Sex Med 2008;5:1805–1816.