The aim of this study was to explore the reasons for improvement in colorectal cancer survival. Trends in relative survival among 5874 patients diagnosed with colorectal cancer over a 24-year period in a well-defined French population were analysed. The 5-year relative survival rate, excluding operative mortality, increased from 49.2% to 56.3% between the periods 1976-1987 and 1988-1999. In multivariate analysis, stage at diagnosis and adjuvant chemotherapy were both associated with better survival after surgery with curative intent. Survival trends differed markedly by age. The improvement in overall survival for older patients can be attributed to the increase in the proportion of patients resected for cure. For younger patients, there was an increase in the proportion of patients operated for cure, but also an improvement in stage-specific survival, particularly for stage III tumours, suggesting an impact of adjuvant chemotherapy.