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After sildenafil, an inhibitor of type-5 phosphodiesterase (PDE5), was put on the Japanese market in March 1999 and then vardenafil emerged later in June 2004, the diagnosis and therapy of erectile dysfunction (ED) has changed dramatically in Japan. However, there have been few studies in the meantime concerning the actual sexual activity in married couples. It has been almost impossible to understand and access the target(s), and the information regarding sex-life between couples in order to establish medical treatment for patients with ED.In the present study, a questionnaire survey was carried out to examine the frequency, periodicity and foreseeability of sexual intercourse and other relevant matters in 300 married couples who had previously revealed that they had sexual intercourse once or more in 3 months.The results obtained clearly show that very few couples have sexual intercourse more than once when the opportunity of intercourse arises, and a majority of them had intercourse at night. Furthermore, the results indicated that more than 80% of the couples could not foresee sexual intercourse 30 min earlier.It was concluded that drugs used to treat ED should be fast acting and make it possible to have sexual intercourse without feeling uncomfortable.