The authors have studied 148 consecutive patients with 170 electrophysiologically confirmed ulnar nerve lesions, who were followed up for one to six years (median 3.8 years) to determine clinical progress and outcome. Injury and intra-operative pressure accounted for 12.9% and 7.1% of lesions respectively; 58.2% were idiopathic with no identified clinical aetiological factor. Eighty-three percent received non-operative treatment initially; 21% of these required operative intervention following further clinical/electrophysiological assessment. Partial or complete recovery occurred in 92% of intra-operative, 64% of idiopathic and 50% of injury cases respectively. Ulnar nerve lesions predominate in males and can be treated non-operatively providing clinical and electrophysiological monitoring is possible. Bilaterality is common and should be excluded. Lesions due to injury have a worse prognosis than those caused by direct continuous or repeated pressure, inflammation or where no aetiological factor exists.