Evaluation of proximal ulnar neuropathy can be a challenging and perplexing electrodiagnostic puzzle. This article focuses on ulnar anatomy and biomechanics to aid in the understanding of possible sites of ulnar nerve entrapment and rationale for differential diagnosis. Discussion of internal nerve topography suggests reasons for ulnar nerve susceptibility at the elbow and offers an explanation for sparing of forearm muscles in ulnar neuropathy at the elbow. Anatomy interfacing with electrodiagnosis illustrates rationale for tests used in evaluating the ulnar nerve. Electrodiagnostic testing enhances localization of ulnar lesions, excludes other etiologies in the differential diagnosis and may aid with surgical selection.