Sexual dysfunctions and difficulties are common experiences that may impact importantly on the perceived quality of life, but prevalence estimates are highly sensitive to the definitions used. We used questionnaire data for 4415 sexually active Danes aged 16-95 years who participated in a national health and morbidity survey in 2005 to estimate the prevalence of sexual dysfunctions and difficulties and to identify associated sociodemographic factors. Overall, 11% (95% CI, 10-13%) of men and 11% (10-13%) of women reported at least one sexual dysfunction (i.e., a frequent sexual difficulty that was perceived as a problem) in the last year, while another 68% (66-70%) of men and 69% (67-71%) of women reported infrequent or less severe sexual difficulties. Estimated overall frequencies of sexual dysfunctions among men were: premature ejaculation (7%), erectile dysfunction (5%), anorgasmia (2%), and dyspareunia (0.1%); among women: lubrication insufficiency (7%), anorgasmia (6%), dyspareunia (3%), and vaginismus (0.4%). Highest frequencies of sexual dysfunction were seen in men above age 60 years and women below age 30 years or above age 50 years. In logistic regression analysis, indicators of economic hardship in the family were positively associated with sexual dysfunctions, notably among women. In conclusion, while a majority of sexually active adults in Denmark experience sexual difficulties with their partner once in a while, approximately one in nine suffer from frequent sexual difficulties that constitute a threat to their well-being. Sexual dysfunctions seem to be more common among persons who experience economic hardship in the family.