Background Survivors of Head and Neck Cancer experience specific problems in functional performance. The aim of this study was to obtain the test-retest reliability of measurements on Maximal Mouth Opening (MMO), shoulder and neck function, lower and upper body strength, level of mobility and walking ability. Materials and methods Test-retest study design. Measurements on MMO (intra-and extra orally), Active range of motion of shoulders and neck, 30 Seconds Chair Stand Test, Grip Strength, Timed Up and Go test, and Six Minute Walk test. Results In total 50 participants were included. The mean age was 68.6. ± 9.9 years and median time since end of treatment was 3.0 years (Q1-Q3: 1.0-5.25 years). We found good to excellent test-retest reliability on the core set of measurements (Intraclass Correlation Coefficient (ICC) 0.77 to 0.98). Measurement of MMO with cardboard card, forward flexion shoulder and Six Minute Walk test had a relatively small measurement error (Smallest Detectable