OBJECTIVES To investigate temporal continuity in ejaculatory dysfunction by comparing self-reported experiences of premature ejaculation (PE) at first intercourse with self-reported PE and delayed ejaculation at present, and to clarify whether and to what extent genetic or environmental factors affect continuity in ejaculatory dysfunction, as previous studies indicate moderate heritability for PE at first intercourse. SUBJECTS AND METHODS The study comprised retrospective self-reported data on ejaculatory performance at first sexual intercourse and a concurrent self-report of the same at the time of data collection in a population-based sample of 2633 Finnish twins and their siblings aged 18-48 years (mean 26.63, sd 4.68). The continuity of ejaculatory function was assessed by correlation and multiple regression. Reasons for continuity were separated into genetic and environmental sources using twin-model fitting. RESULTS Ejaculatory function, particularly PE, was stable over time. Genetic effects accounted for approximately 30% of the variance in PE both at first intercourse and when measured at data collection. Unshared environmental effects accounted for most of the variance ( approximately 70%). Genetic effects were almost identical between the sample occasions, but there was a substantial discrepancy between unshared environmental effects affecting PE at first intercourse and unshared environmental effects affecting PE later in life. Age effects were generally negligible. Data were self-reported and retrospective, and thus vulnerable to response bias. CONCLUSIONS Ejaculatory dysfunction seems to be temporally stable both in the short and long term. Genes that contribute to the variance in PE at first intercourse are similar to those that contribute to the variance in PE later in life, whereas there are, in this regard, substantial differences in the unshared environmental factors that are a cause of PE.