The variability of nutrient intake within individuals has been examined using data from a 7‐d weighed inventory record from a population sample of 164 middle‐aged men. Four main aspects of within‐person variation were examined: variation according to day of the week, daily variation as a proportion of individual mean values, daily variation in relation to betweenperson variation, and long‐term variation, in mean daily intake.The intake of some nutrients showed a significant day of the week variation, but apart from alcohol and energy, most of these variations were small. The within‐person coefficient of variation generally showed wide ranges for most nutrients.To assess the individual intake of 90% of the men, to within a s.e. of 10% a weighed record of seven days was sufficient for the calculation of the percentage of energy derived from protein, fat and carbohydrate, but not for nutrients such as linoleic acid and fibre. Seven days was adequate to classify 80% of these men into their appropriate third of true rank order of intake for all dietary constituents studied, except for amounts of linoleic acid and cholesterol.Considerable long‐term stability in mean nutrient intake was shown in the 30 men who completed a 7‐d weighed record after a period of two years but evidence of long term changes in dietary habit w