Early menarche has been associated with higher risk of breast cancer. A prospective study has been conducted in Quebec City, Canada, to evaluate the relationship of dietary intake to age at menarche. On three occasions during the schoolyear 1986-87, 2,299 pre-menarche. Incidence density ratios (IDRs) adjusted for age at entry and mothers' age at menarche were computed using proportional hazards models. IDRs for quartiles of energy, nutrient and food-group intakes were not different from the null value. In this population of well-nourished girls, diet did not influence the age at onset of menarche.