This paper summarises the scientific evidence supporting selection of risk groups that would benefit from annual seasonal influenza immunisation in European Union (EU) countries. Risk groups are defined restrictively as persons in Europe at higher than average risk of adverse outcomes should they be infected with seasonal influenza and for whom use of vaccine is demonstrated to be effective in reducing the risk of those outcomes. Existing evidence indicate that older people and those with chronic disease are at higher risk of severe adverse outcome and that immunisation reduces this risk. There is thus good scientific evidence for routinely offering annual immunisation to all older people (at least those aged 65 years and older), and people with certain groups of chronic medical conditions. We estimated that these two groups account for between 19% and 28% of the population of EU countries. Thus in 2006, an estimated 84 million older people aged 65 years and over and 41 million people younger than 65 years of age with chronic conditions were living in these countries. There is also strong evidence for immunising staff caring for patients belonging to these two risk groups in residential (care home) settings in order to protect the patients. There are as yet no strong data on whether or not immunising other healthcare workers and carers protect patients though immunisation of healthcare workers can be justified on occupational health grounds. At present the scientific evidence for immunising other suggested risk groups, notably children and pregnant women is not strong for Europe though equally there is no evidence against immunising these groups.