ABSTRACTDermatomal somatosensory evoked potentials (DSEPs) have been used in the diagnosis of patients with compressive radiculopathies. Several investigators have reported yields high enough to warrant the possible clinical use of dermatomal SEPs in the identification of lumbar root entrapment; however, the test is relatively insensitive. Since the validity and the utility of dermatomal SEPs remains controversial, the purpose of this investigation is to test the hypothesis that the routine clinical documentation of dynamic lumbosacral nerve root pathology may be complemented by dermatomal SEPs. We studied the clinical, electrophysiological, and neuro-imaging features of ten patients in whom DSEPs added significant data to the work-up of either unilateral compressive radiculopathy or in more complex structural problems involving herniated disc pathology plus a tethered cord (two cases). Technical methodology and waveform analysis, in particular the latency of N1 as defined by onset of downward slope from baseline to P1, illustrated the reliability of DSEPs in both our normal and abnormal populations. DSEPs show a limited potential for improving upon a standard electrodiagnostic evaluation. We suspect that the neural generator for the N1 waveform lies within the primary somatosensory cortices on the medial surfaces of the postcentral gyri.