Background: Cancer cachexia is associated with poorer outcomes and is often diagnosed by the Fearon criteria. Oncologists clinically identify cachexia based on a patient’s presentation. In this study agreement between these identification methods was evaluated and associations with outcomes were studied in patients with metastatic colorectal cancer. Methods: Fearon criteria comprised weight loss >5% OR weight loss >2% with either BMI <20 kg/m2 or sarcopenia (determined by CT-imaging). Clinical assessment by the oncologist was based on the patient’s clinical presentation. Agreement was tested with Kappa. Associations with treatment tolerance and progression free survival (PFS) were tested with logistic regressions and Cox proportional hazards, respectively. Results: Of 69 patients, 52% was identified as cachectic according to Fearon criteria and 9% according to clinical assessment. Agreement between both methods was slight (Kappa 0.049, P = 0.457). Clinically cachectic patients had a shorter PFS than clinically non-cachectic patients (HR 3.310, P = 0.016). No other differences in outcomes were found between cachectic vs. non-cachectic patients using both methods. Conclusions: The agreement between cancer cachexia identification by clinical assessment vs. Fearon criteria was slight. Further improvement of cachexia criteria is necessary to identify cachectic patients at risk of poorer outcomes, who may benefit from targeted cachexia interventions.