44 Abstract Background Treatment of patients with head and neck cancer can result in disrupted mastication. To measure masticatory performance in people with compromised mastication, the Mixing Ability Test (MAT) was developed. In this study, the reliability of the MAT was evaluated in patients with head and neck cancer and healthy controls. Methods Thirty-four patients with head and neck cancer and 42 healthy controls performed the MAT twice on the same day. To assess reliability, the Intraclass Correlation Coefficient (ICC2,1), Standard Error of Measurement (SEM), Smallest Detectable Change (SDC), and Limits of Agreement (LoA) were calculated. Results A good (ICC=0.886) and moderate correlation (ICC=0.525) were found for patients and healthy controls, respectively. Patients had a worse mixing ability (mean=19.12, SD=4.56) in comparison to healthy controls (mean=16.42, SD=2.04). The SEM was 0.76 in patients, and 1.45 in healthy controls, with a SDC of 2.12 and 4.02, respectively. The LoA were - 4.46 to 4.42 in patients, and -3.65 to 4.59 in healthy controls. Conclusion The MAT has a good reliability in patients with head and neck cancer and a moderate reliability in healthy controls.