It is common to use a demand systems approach in estimating the key parameters from household consumption data. In conducting these studies the researcher is faced with selecting a functional form. In turn, each functional form implies a particular shape for the Engel curves. This analysis highlights the importance of testing the shape of Engel curves, especially if the researcher is interested in elasticity estimates well away from the sample mean. Using consumption data for selected households in Italy it is shown that many popular functional forms are rejected by the data.