Introduction: Modified Ashworth scale (MAS) is commonly used for assessment of muscle tone in clinical practice. Different degrees of reliability were discovered in previous reliability studies, which may also be due to the lack of a standardized testing protocol. Range of motion measurements are also used for assessment of muscle tone. Purpose: To evaluate intra- and interrater reliability of MAS. To investigate the relationship between MAS grades and joint range of motion and muslce strength of plantar and dorsal flexors. Methods: Thirty patients after stroke were included. Reliability was assessed between three raters. We assessed six muscle groups in upper limb and six muscle groups in lower limb, with the protocol, established on the basis of previous studies. Joint range of motion was measured in supine with universal goniometer. We also measured ankle dorsal flexion in standing position with gravity goniometer. Muscle strength measurements were assessed with hand-held dynamometer. We calculated intraclass correlation coeficient (ICC) for reliability assessment. Spearman's rank correlation coefficient was calculated for assessment of correlation between MAS grades and joint range of motion and muscle strength of plantar and dorsal flexors. Results: Results demonstrated moderate to excellent (ICC = 0,60–0,99) intrarater reliability. Interrater reliability was poor to good (ICC = 0,32–0,86) when assessing upper limb and poor to moderate (ICC = 0,41–0,65) when assessing lower limb muscles with MAS. MAS grades negatively correlated with joint range of motion (ρ = –0,72– –0,36). MAS grades of m. triceps surae and m. soleus negatively correlated with muscle strength of m. triceps surae (ρ = –0,43– –0,42) and dorsal flexors (ρ = –0,5– –0,45). Discussion and conclusion: Reliability of MAS differs among different muscles being graded. We recommend that muscle tone assessment is performed by the same therapist at the beginning and end of rehabilitation, based on higher levels of intrarater reliability than interrater reliability. Results of relationship between MAS grades and joint range of motion and muscle strength are in concordance with previous research and show that high muscle tone is associated with shorter range of motion and lower muscle strength.