We consider the effects of demographic and expenditure variables on consumer demand in a system of Engel curves using a smooth coefficient semiparametric model, where the expenditure effects on the budget shares vary nonparametrically with continuous demographic variables such as age of head and number of children. Our findings based on UK micro data suggest that with a smooth coefficient semiparametric model there is no need for nonlinear logarithmic expenditure effects in the budget shares.