OBJECTIVES: Inequalities in life expectancy between the most and least materially deprived areas in the province of Quebec, Canada are increasing, but the reasons for this trend are unclear. An analysis of which causes of death, in which age groups, are implicated in this trend is necessary to understand it and provide clear targets for intervention. METHODS: We analyzed Quebec mortality data for three 4-year periods from 1989-2004. Differences in life expectancy at birth between the most- and least-deprived areas in each period and over time were decomposed by age and cause of death for men and women using the Arriaga method. RESULTS: Life expectancy increased for all areas, but the increase was smaller in deprived areas. Cancer, heart disease and unintentional injuries accounted for the largest shares of inequality in each period. Among women, the widening life expectancy gap was largely due to increased lung cancer mortality. Among men, mortality from HIV was an important cause of widening inequality. Increasing inequality in both sexes was offset by a decrease in mortality from unintentional injuries in deprived areas (narrowing the gap between the most- and least-deprived areas). The largest share of inequality among women was due to deaths in the 65-and-over age group. Among men, the largest share shifted over time from middle-age to the 65-and-over age group. CONCLUSION: The widening life expectancy gap between advantaged and disadvantaged areas in Quebec is driven by relatively few causes of death with well-known risk factors and strategies for prevention.