BACKGROUND: Prescription drug expenditures in North America have nearly doubled in the past 5 years, creating intense pressure for all public and private benefits managers and policymakers. OBJECTIVE: The objective of this study was to describe age-specific drug expenditure trends from 1996 to 2002 for the Canadian province of British Columbia. STUDY DESIGN: This study shows changes in expenditures per capita quantified for 5 age categories: residents aged 0 to 19, 20 to 44, 45 to 64, 65 to 84, and 85 and older. The cost impacts of 7 determinants of prescription drug expenditures are quantified. DATA: This study describes population-based, patient-specific pharmaceutical data showing the type, quantity, and cost of every prescription drug purchased by virtually all residents of British Columbia. RESULTS: Population-wide expenditures per capita grew at a rate of 11.6% per annum. Growth was primarily driven by the selection of more costly drugs per course of treatment and increases in the number concomitant treatments received per patient. Population aging did not have a major impact on expenditures. However, expenditure per capita grew most rapid among residents aged 45 to 64, the cohort that expended most over the period. The aging of this demographic cohort may threaten the financial viability of age-based drug benefit programs.