Several uncertainties surround optimal management of colorectal cancer. We investigated treatment patterns and factors influencing treatment receipt and mortality in routine clinical practice. We included 15 249 individuals, recorded by the National Cancer Registry (Ireland), with primary invasive colon or rectal tumours, diagnosed during 1994-2002. Logistic regression and Cox proportional hazards were used to determine factors associated with treatment receipt within 1 year of diagnosis and with mortality, respectively. A total of 78% had colorectal resection, 31% chemotherapy, and 13% radiotherapy (4% colon; 28% rectum). Half of stage IV patients underwent resection. Chemotherapy and radiotherapy use increased by at least 10% per annum. There was a notable increase in pre-operative radiotherapy from 2000 onwards. Patient-related factors were significantly associated with treatment receipt. Patients who were male, older, not married, or smokers had significantly higher risks of death. Chemotherapy was significantly associated with lower mortality for stage III, but not stage II, colon cancer. For rectal cancer, pre-operative radiotherapy was associated with reduced mortality. Surgery and chemotherapy were associated with longer survival for stage IV patients. The observed inequities in treatment and outcomes suggest that there is potential for further dissemination of therapies in routine practice. Improving treatment availability overall, and equity, has the potential to reduce mortality.