Abstract The degree of instrumentality and expressiveness displayed by males and females is known to correlate with a wide range of behaviors. A number of studies have investigated the impact of these personality traits on sexual strategy selection, in particular partner preference. Here we report associations between the lifetime number of sexual partners and the age at first sexual intercourse in relation to personality (as measured by the Bem Sex Role Inventory; BSRI) in a sample of 232 German males and females aged 16–63 years. Significant sex differences were found for BSRI measures such that males scored higher on instrumentality, while females scored higher on expressiveness. Significant positive associations between BSRI instrumentality scores and the reported lifetime number of sexual partners were found in both males and females. In addition, reported age of first sexual intercourse was negatively correlated with BSRI instrumentality scores in males. Finally, females scoring higher on BSRI instrumentality reported to have more lifetime number of sexual partners, even when actual biological age was controlled for. These findings suggest that there are significant within-sex differences in sexual behaviors due to the possession of instrumental personality traits.