Aim:
The purpose of this research was to explore the subject of sexual activity in the Polish population, with special focus on age and gender differences, and sexual infidelity. Sexual activity is one of the basic factors in initiating and maintaining relationships. On the one hand, sexual activity enables us to meet natural needs and maintain an intimate relationship with another human being; on the other, it may allow us to overcome loneliness and social isolation by providing the opportunity to express feelings of closeness and unity.

Material and Methods:
The research was conducted on a representative group of 3,200 Poles aged between 15–49, with the support of a well-known Polish research company – TNS OBOP. Face-to-face and Pencil and Paper (PAPI) interviews were carried out.

Results:
The results focus on two main issues: the age and motives of sexual initiation among teenagers (with a significant percentage starting their sexual activity at the age of 15), and the quality of the sexual lives of adults (average number of sexual partners, sexual infidelity and sexual satisfaction).

Conclusions:
There is dependence between the type of relationship and the performance or non-performance of sexual activity, as well as the quality of the relationship. Among both adolescents and adults, remaining in a stable relationship (partnership or marriage) promotes loyalty. The performance of sexual goals turns out to be an important mechanism regulating the interpersonal aspects of a relationship, influencing their perception and evaluation.