This is a sexological study of a random sample of 225 40-yr-old women representative of the Danish female population at the age of 40. These women were questioned by a female physician utilizing a structured interview; 94% of the women invited to participate in this study agreed to do so. The purpose of this research was to elucidate sexual behaviour, experience, knowledge and attitudes. Some of the findings were the following. Menstruation still seems to be a taboo subject; 36% of this population knew little about this topic. 96% of these women had experienced orgasm at least once in their lives and 67.6% had experienced spontaneous libido. Genuine homosexuality appears to be a rare phenomenon. A monogamous heterosexual life style is the norm, as reflected by low number of partners and low frequency of infidelity. Yet, 35% of these woman had sexual problems. There is a need for advice and treatment of sexual difficulties in this population, but these are at present, in Denmark, not generally available.