For 10 years, a prospective study has been taking place in Germany to examine the use of natural family planning (NFP). As natural methods are behavioral methods, use-effectiveness, acceptability and continuation rates are very much influenced by patterns of sexual behavior. Therefore we performed an analysis of the sexual behavior of NFP users. Out of the data base of 1211 clients and 12,591 cycles we could identify a group of 300 women, all NFP beginners, with 5900 contraceptive cycles, who contributed at least 12 cycles with reliable recording of their sexual activity. Different groups were analyzed with methods of analysis of variance and regression models to find out significant differences in their sexual behavior with respect to sociodemographic structure and time of use. Nearly half of all the women systematically combine the fertility awareness part of NFP with other family planning methods. They use barriers in more than 60% of their cycles. The other half never or only in about 7% of their cycles use additional barrier methods. The latter show a clear decrease in barrier use in the course of time, whereas the frequent barrier users constantly combine the advantages of two family planning methods. Regarding the frequency of intercourse they are the sexually more active ones and show distinct sociodemographic characteristics. We could confirm the existence of three groups of NFP users, which differ significantly in their use of NFP as a family planning method. Despite these differences the low pregnancy rates indicate the conscious and risk-related sexual behavior of the group members.