Both jurisdictions of Ireland have high rates of chronic degenerative diseases, particularly of the cardiovascular system, and Irish migrants have worse health profiles, often lasting at least two generations. The influence of socio-demographic variation over the life course, and what role diet plays, has not been well researched in epidemiological terms. There is a long history of an unusual Irish diet. Estimated dietary fat intake (% total energy intake) in 1863 was only 9, but had reached 30 in 1948 and 34 in 1999. Conversely, carbohydrate intake has fallen steadily over 150 years. From 1948 onwards household budget survey data illustrate patterns of increasing urbanisation and socio-economic gradients in food availability. The National Survey of Lifestyles, Attitudes and Nutrition, (n 6539, 622 % response rate) provides clear evidence of inverse social-class gradients in intake of fruit and vegetables and dairy products and in reported patterns of healthy eating. Median carbohydrate and vitamin C levels are higher among social classes 1-2 and mean saturated fat intake is lower. International comparisons indicate a continuing, if narrowing, north-south gradient across Europe. Data from the Boston-Ireland study suggest a crossover in both dietary intake patterns and risk of heart disease in Ireland and the USA in the 1970s. Contemporary comparative data of middle-aged Irish and American women demonstrate patterns of diet intake and inactivity consistent with the modern epidemic of obesity and non-insulin-dependent diabetes. Thus, dietary variations within and between countries and over time are consistent with chronic disease patterns in contemporary Ireland.