Objective: To describe abnormal electrophysiological findings in patients with low back pain referred to electromyography (EMG) examination in a public hospital in Bogota, Colombia. Materials and Methods: we reviewed the electrophysiological studies of 569 patients referred to electrodiagnostic evaluation over an three years periodo Abnormal findings were registered in vastus medialis, tensor fascia lata, anterior tibialis, tibialis posterior, medial gastrocnemius, lateral gastrocnemius, g1uteus maximus and lumbosacral paraspinal muscles. Results: Among the 203 abnormal studies (35.67%),103(18.1 %) were probable and 100 (17.5%) were defmitive. Most of the patients ranged in age from 40 to 60 years. EMG abnormalities were frequently found in oldest patients (mean 55.6 years in contrast to 50.5 years in youngest patients P=0.000) most of them were males (P=0.003). Muscles that showed abnormalities were lumbosacral paraspinal, (85 individuals 14.9%) and tibialis anterioris (99 individuals 17.4 %). The proportion of EMG abnormalities between these groups of muscles didnt show significant differences (p=0.46) but these muscles correlated with vastus medialis and gastrocnemius (medial and lateral) had statistically significant differences. Conclusions 1.EMG abnormalities in patients with low back pain were much higher in oldest male patients. 2. EMG abnormalities were frequently observed in tibialis anterior and paraspinal muscles. 3. Electrophysiological studies showed a lower number of anormalities compared with other reports, probably the reasons were: a. Different criteria of abnormalities, (only definitive studies were cousidered) excluding reinervation evidence.b.The number of muscles examined in each patient was lower than those recommended in other investigations. c.The clinic criteria of reference were not adecuated.