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Carpal Tunnel Syndrome (CTS) is the most common entrapment neuropathy of the upper extremity. A dilemma that plagues surgeons is the patient with clinical evidence of CTS who seeks immediate corticosteroid injection prior to confirmatory electrodiagnostic studies. If such is the case, cortisone injections given prior to electrodiagnostic testing may alter the results and lead to changes in management, which would not have been otherwise considered. The purpose of this study is to determine whether the potential change in nerve conduction testing following steroid injection is statistically significant in patients with CTS. One hundred forty-five (145) patients with suspected CTS were targeted for this study. Twenty-seven (27) patients underwent pre- and post-injection testing. Repeat studies were performed 4-6 weeks after injection. All data obtained from electrodiagnostic studies were entered into a database and used for comparison. The average distal motor latency prior to injection (DML1) was 5.01 +/- 0.9 ms and the average peak sensory latency prior to injection (PSL1) was 5.01 +/- 0.88 ms. The average distal motor latency after injection (DML2) was 4.82 +/- 0.7 ms and the average peak sensory latency after injection (PSL2) was 4.69 +/- 0.66 ms. The mean difference between DML1 and DML2 was 0.187 +/- 0.45 ms and the mean difference between PSL1 and PSL2 was 0.319 +/- 0.48 ms. Both were found to be statistically significant using the paired T-test. Based on this study it is shown that there is a statistical difference between testing done before and after steroid injection and that injections given prior to electrodiagnostic testing will alter the results and may affect patient management. Thus our recommendation is that nerve testing be performed prior to steroid injections so that an accurate grading of severity can be made of the patient’s current disease. This would allow for more consistent guidance in management of the patient’s CTS.