OBJECTIVE: To utilize international patient reported outcomes (PROs) data and identify the size and impact of patient populations suffering from insomnia/sleep difficulty in four countries: United States, United Kingdom, France, and Germany. METHODS: An annual, self-reported study of consumer attitudes and behaviors conducted by Consumer Health Sciences was fielded in June, 2004 and completed by 60,050 adults, 18 years of age or older in the United States (40,736), United Kingdom (8,393), France (9,011), and Germany (9,064). We stratified and weighted the sample by key demographics. All respondents were asked if they experienced insomnia or sleep difficulty within the past 12-months and if they had their condition physician diagnosed. Respondents also completed the SF-8 and the WPAI. RESULTS: Of the 374.0 million adults in the four countries examined, 27% (101.8 million) reported to have experienced insomnia/sleep difficulty in the previous 12-months. The number of insomnia/sleep difficulty sufferers in the United States is 53.2 million, 51% of total number of sufferers, while the number of insomnia/sleep difficult sufferers in the United Kingdom, France and Germany combined is 48.6 million adults, 49% of total number of sufferers. Diagnosed insomnia/sleep difficulty sufferers in the UK have the lowest SF-8 Mental health score: 39.2 and the lowest SF-8 Physical health score: 37.9 (p<0.05). The percentage of insomnia/sleep difficulty sufferers who missed work due to their health 26% or more of the time was highest in France:25.5% and lowest in the United States: 12.7% (p<0.05). CONCLUSIONS: Insomnia/sleep difficulty remains a significant health care issue for adults in the United States, United Kingdom, France and Germany. The impact that insomnia/sleep difficulty has on the quality of life and productivity of adults warrants further investigation for public policy makers and health care officials.