Introduction This study was undertaken to assess the intra-and interrater reliability of sonographic thickness measurements of the thenar and hypothenar muscles. Methods: The thickness of the thenar and hypothenar muscles of both hands of 15 volunteers (7 male, 8 female) were evaluated with a 4-13-MHZ linear probe by 2 examiners who were blinded to each other's measurements. Interrater reliability was then evaluated. To assess intrarater reliability, the first examiner also performed a second measurement after an interval of at least 1 day. Results: Mean age of the subjects was 31.169.0 years. Test-retest reliability showed excellent intrarater reliability (intraclass correlation coefficient range: 0.889-0.963) and substantial to excellent results for interrater reliability (intraclass correlation coefficient range: 0.692-0.937). Discussion: We found that ultrasound is a reliable method for thickness measurements of the thenar and hypothenar muscles.