In this retrospective study the authors have analysed the results of electrophysiologic examinations in patients with paresis or paralysis of the foot dorsiflexors. Two groups have been distinguished. A first group consists of 217 patients, investigated between April 1st 1986 and September 30th 1987. Several etiologic categories have been recognized and the relative frequency of each of them in the group as a whole has been described. Footdrop has been found to be either of central neurogenic origin (31%) or of peripheral neurogenic origin (68%). The latter group has been further subdivided, the most important subgroups being common peroneal nerve lesions (30.6%), L5-radiculopathies (19.7%) and polyneuropathies (18.3%). In a second group, the authors have studied the results of 34 electrophysiologic examinations for footdrop due to a sciatic nerve lesion and of 109 examinations for footdrop due to common peroneal nerve palsy. The period covered was from January 1st 1980 to September 30th 1987 The authors have been able to draw a parallel between these two categories of footdrop patients; 76.5% of the sciatic nerve lesions and 67.0% of the common peroneal nerve lesions are traumatic in origin; in both groups there is a striking preponderance of young male patients, which is even more pronounced when only the traumatic lesions are considered. In the majority of cases with sciatic nerve damage the peroneal portion is involved. In the common peroneal nerve lesions, the deep structures are more frequently injured than the superficial aspect.2=