Sexual activity is an important dimension of quality of life. Therefore it is important to assess the impact that any treatment may have on sexual functioning so that patients can be warned of possible side effects and interventions offered to help ameliorate these. The Sexual Activity Questionnaire (SAQ) was developed to investigate the impact of long-term tamoxifen on the sexual functioning of women at high risk of developing breast cancer. It was also tested on a sample of women with no such risk. The majority of variance in sexual functioning can be explained by three factors: pleasure from sexual intercourse, discomfort during sexual intercourse and habit. We found that the frequency of sexual activity decreased steadily with age. Furthermore, pleasure dropped and discomfort increased in women aged over 55. We report psychometric data showing that the SAQ is a valid, reliable and acceptable measure for describing the sexual functioning of women in terms of activity, pleasure and discomfort. It is quick and easy to administer and has good face validity discriminating between the sexual functioning of pre- and post-menopausal women.