OBJECTIVES: Monoclonal antibody treatments for metastatic colorectal cancer (mCRC) have different treatment-related toxicities. This study aimed to elucidate the hospitalisation costs of adverse events (AEs) commonly associated with monoclonal antibodies when administered to patients with mCRC. METHODS: This study extracted data for patients newly diagnosed with mCRC from a large US claims database from January 2005 to June 2008. The first distant metastasis diagnosis date was defined as the index date. Hospital admissions for AEs of interest were identified by primary discharge diagnoses after the index date. Main outcomes were mean length of hospital stay (days) and hospitalisation costs (US$) per hospital admission for AEs identified. All analyses are presented descriptively. RESULTS: The study population (aged ≥18 years; n=12,648) was balanced according to gender and was mainly aged 50 years or older (90.1%). Most patients had colon cancer (70.1%) as opposed to rectal cancer. The longest mean (median) length of stay was observed for Wound-healing complications (14.1 (7.0) days) and gastrointestinal (GI) perforation (13.8 (11.5) days), followed by hypertension (8.5 (3.0) days), arterial thromboembolism (7.1 (5.5) days), venous thromboembolism (5.4 (4.0) days), and congestive heart failure (5.3 (4.0) days). The highest inpatient cost per event was for GI perforations (mean $66,224 and median $34,027), followed by arterial thromboembolism (mean $40,992 and median $18,587), wound-healing complications (mean $36,440 and median $21,163), interstitial lung disease (mean $26,705 and median $19,111), and acute myocardial infarction (mean $22,395 and median $15,223). Skin toxicity (mean $6,475 and median $6110) was associated with relatively low costs. CONCLUSIONS: Hospital costs for monoclonal antibody treatment-related AEs in patients with mCRC vary greatly. This study provides source data for economic evaluations of head-to-head comparisons of monoclonal antibody treatments.