Using the Female Sexual Function Index (FSFI) for investigating female sexual function has become widespread. A score of 26.5 has been suggested as delineating 'functional' from 'dysfunctional' women. This study aimed to understand in greater detail what contributes to changes in women's FSFI scores while their partners are taking oral erectile medications for erection problems. Couples randomized to receive two erectile medications for two 3-month phases, completed questionnaires. FSFI scores were augmented by individual interviews at baseline, 3 and 6 months, in order to better understand what the scores meant in the context of ED medication use. In all, 50% of the women scored o26.5 at baseline; of these 56% recovered by 6 months. A number of 'dysfunctional' women recorded low FSFI scores solely as a result of their partner's ED. Overall, 22% were still 'dysfunctional' at 6 months, but one third of these appeared 'functional' at 3 months. A further group of women continued to record low scores despite reporting much improved sexual satisfaction. The women's interviews elaborate on their FSFI results, with five themes emerging to provide more clarity about the relative changes seen in a prospective study situation, and potentially in clinical practise contexts. The increasing use of questionnaires to determine sexual function should be supplemented with good clinical interviewing. The interview details explain how FSFI fluctuations occurred and contain clinical implications for research and practise in the area of couple's sexuality. 14-16 Women with FSFI scores concomitant with sexual dysfunction (o26.5) were excluded from some studies because of the potential of such 'dysfunction' to have a negative impact on the effect of men's ED treatments on the couples. 10,11 However, a recent treatment study, that included all women regardless of their dysfunctional status, reported that once the man's ED had been effectively treated the putative 'dysfunction' was no longer present in many of the women. 16 Although these reports, based on the standardized measures, detail overall changes in the women's sexual function as their partners were treated, they do not describe why the women experience improvement in their sexual function.Several studies reporting women's sexual function changes during their partner's ED treatment show disparities in the effects on women of treating men's erection problems. In studies employing the FSFI, domains in which improvement has been reported include arousal, lubrication, orgasm, satisfaction and overall scores. 11,16,17 Although the 16 both reported improvements in women's levels of pain once their partner's ED was treated. The findings from the FEMALES study may have been influenced by it being retrospective and excluding women reporting pain at baseline. The present prospective study, which included all women, irrespective of their FSFI score, sought to clarify the extent to which the problems reported by female partners of men with ED are the result of the man's ED or other factors...