A psychological investigation was implemented to find out if NFP users are characterized by special personality traits and if there are any correlations between NFP practice and changes within the marriage partnership. A total of 258 NFP users, both women and men, were investigated with questionnaires of the type generally used in the field of personality research in the Federal Republic of Germany, and also with questionnaires concerning the partnership and attitudes toward pregnancy, sexuality, and childbirth. It was found that with respect to personality traits, the NFP user does not differ considerably from people designated as "normal population." Only their attitudes toward sexuality are more positive and uninhibited, and the women feel less subjectively helpless than the standard sample. Furthermore, there is a connection between increased NFP experience and changes within the partnership, in that there is a reduction of "dominant" attitude (in both men and women) with growing NFP experience. Couples with long NFP experience and NFP beginners have nearly the same degree of well-being between the partners, whereas couples who have just passed the learning phase show more ill-feeling between husband and wife. Factors concerning the partnership account much more for the differences in marital satisfaction than do sociodemographic variables or personality traits.