Although rising food prices have hit hard on a large number of households in many developing countries, the vulnerability in terms of food security varies across different household sectors within a country. In this study we have developed a simple analytical model and used it to examine the food security vulnerability across different households to a shock in food prices by using three commonly-known household sectors (urban, rural, estate)in Sri Lanka. In particular, we have estimated the combined impact of income and price rises on food security of these sectors. Our empirical results suggest that the overall food security in all three household groups (measured in terms of real food consumption above the poverty line food consumption) has been marginally decreasing over time in Sri Lanka. Furthermore, the negative effect of rising food prices has been partially offset by the positive income effect in all three household sectors. The results also suggest that the urban sector is highly vulnerable to a food price shock than the other two sectors. The least vulnerable group is the rural sector, whilst the estate sector lies in the middle.