The Australian Study of Health and Relationships is a large national population-representative survey of sexual behavior and attitudes conducted every decade. We describe experiences of sexual difficulties lasting at least a month among Australians surveyed in 2012-2013 and identify changes since the previous survey in 2001-2002. Computer-assisted telephone interviews were completed by 20,091 people aged 16-69 years (participation rate 66%) of whom 16,897 people had had sex with a partner in the previous year. We asked how long each difficulty lasted, whether it was a problem, and whether they sought treatment. Half (48%) the men and 68% of women reported at least one difficulty. Lack of interest in having sex was common (28% men, 52% women); 21% of men reported coming to orgasm "too quickly" and women reported inability to reach orgasm (25%) and trouble with vaginal dryness (22%). Women were more likely than men not to find sex pleasurable and to have physical pain during intercourse. Some differences by age group were also apparent. Many difficulties were not seen as problems, especially lacking interest and reaching orgasm too quickly. People with erection/dryness problems, or with pain in intercourse, were more likely to seek treatment, as were people with multiple difficulties. Between 2001-2002 and 2012-2013, there was little change for men, but among women rates of all sexual difficulties fell by 4-10 percentage points. This change accompanied a drop in frequency of sex among people in ongoing relationships and an increase in masturbation and use of pornography. One explanation might be that, over time, fewer women were agreeing to "service sex" when they were not in the mood. Overall, the drop in prevalence of women's sexual difficulties since a decade earlier suggests a change towards more egalitarian sexual relations.