This article discusses two aspects of using daily expenditure records, commonly referred to as diaries, in a household expenditure survey, based on the experience of the 1979–1980 Hong Kong Household Expenditure Survey. In particular, the article investigates the determinants of the decision by individual household members to fill out diaries, conditional upon the household having agreed to participate in the survey. In addition, estimates are presented of the additional reporting that results from household members keeping individual diaries, as opposed to one member keeping one household diary book.