AIMS: The Avastin(®) Registry - Investigation of Effectiveness and Safety (ARIES) observational cohort study (OCS) was designed to prospectively examine outcomes associated with bevacizumab-containing treatment for metastatic colorectal cancer (mCRC) in a community-based setting, where patient populations are less restricted than those in randomised trials. MATERIALS AND METHODS: Patients with mCRC who were eligible for bevacizumab in combination with chemotherapy in first- or second-line treatment were enrolled from November 2006 to September 2008. There were no protocol-specified treatment regimens; the dose and schedule of bevacizumab and chemotherapy were at the treating physician's discretion. The objectives in the ARIES OCS included analyses of progression-free survival (PFS), overall survival, treatment patterns and safety in each of the first- and second-line treatment cohorts. RESULTS: ARIES enrolled 1550 patients with mCRC receiving first-line therapy with bevacizumab. The median follow-up time was 20.6 months. The median PFS in this cohort was 10.2 months (95% confidence interval 9.8-10.6) and the median overall survival was 23.2 months (95% confidence interval 21.2-24.8). In a separate cohort of 482 patients with second-line mCRC, the median follow-up time was 16.9 months, the median PFS and overall survival from the start of second-line treatment to the end of follow-up was 7.9 months (95% confidence interval 7.2-8.3) and 17.8 months (95% confidence interval 16.5-20.7), respectively. Incidences of known bevacizumab-associated adverse events in ARIES were generally consistent with those previously reported in OCSs and randomised trials. CONCLUSION: Results from the prospective ARIES OCS add further evidence to support the effectiveness and safety of bevacizumab when added to first- and second-line treatment regimens for patients with mCRC in community treatment settings.