Reliable techniques to assess centrally mediated function in healthy individuals are essential to understand the origins of neuromuscular dysfunction in pathologic populations. This study examined the test-retest reliability of corticospinal excitability in the upper extremity musculature of 21 healthy individuals using transcranial magnetic stimulation. Within-session reliability was assessed by comparing tests performed 120 minutes apart. Between-session reliability was assessed by comparing the second (24 hr), third (1-week), and forth (2-week) sessions to the first test. We recorded active motor threshold (AMT) and motor evoked potential (MEP) at 120% AMT of the upper trapezius (UT), middle deltoid (MD), and flexor carpi radialis (FCR) bilaterally. Intraclass correlation coefficients (3,1) were used to assess relative reliability, and minimal detectable changes at 95% confidence level were calculated to assess absolute reliability. Our results suggest that AMT of the MD and FCR demonstrated acceptable within-session and between-session reliability over 24 hours, with all muscles evaluated ranging from moderate to good over 2 weeks. In contrast, MEP amplitudes were less reliable for all muscles, with reliability point estimates ranging from poor to moderate. AMT appears to be a more consistent measure of corticospinal excitability in upper extremity musculature, which may be more appropriate in clinical outcomes research.