The dopaminergic system in the brain seems to play an important role in the regulation of sexual behaviour. The relationship between genes for the D1, D2 and D4 dopamine receptors and age at first sexual intercourse (AFSI) was examined in a sample of 414 non-Hispanic, European–American men and women. A significant association was observed between a DRD2 allele and AFSI and an even stronger association when the DRD2 allele was interacted with a DRD1 allele. A constrained regression model was constructed predicting AFSI using sex and a group of nine psychosocial variables as predictors. Adding the DRD2 and the DRD2-by-DRD1 predictors to this model increased the explained variance by 23 and 55%, respectively. Although these findings suggest a stronger association among males than among females, further research will be necessary to clarify this question, as well as to establish whether the observed association holds in other racial/ethnic groups.