Although premature ejaculation (PE) is a common type of male sexual dysfunction, to date we lack a unified definition of PE. The multidimensional definition of PE has been accepted by more and more clinicians. Intravaginal ejaculatory latency time (IELT) is one of the three important dimensions (time to ejaculation, inability to control or delay ejaculation, and negative consequences) for defining PE. Rapid ejaculation is one of the core symptoms of PE and IELT is an objective measurement as well as an important tool for the evaluation of PE. This article reviews estimated IELT, stopwatch-measured IELT, the correlation between estimated and stopwatch-measured IELT, and the factors affecting IELT in the general male population, PE patients, and those complaining of PE.