The purpose of this study was to identify aetiological factors that may determine prognosis in ulnar nerve lesions at the elbow and to evaluate the role of non-operative treatment. One hundred and thirty consecutive patients (92 male) with 152 electrophysiologically proven (by nerve conduction and electromyography) ulnar nerve lesions at the elbow were identified from the departmental records. Patient details, symptoms, known aetiology and treatment profile were recorded. Each patient was then contacted by telephone and / or questionnaire between one and six years after electrodiagnosis to determine clinical progress and outcome. In patients with sensory symptoms alone or non-progressive painless motor symptoms, non-operative treatment was commenced. This involved advice on activity modification and protection with a tubipad bandage or night splint with continued clinical and electrophysiological surveillance. Sixty-one percent of lesions were idiopathic with no clinical aetiological factor. Defined causes included deformity and/or synovitis from arthritis of the elbow (11.2%), injudicious intra-operative pressure (9.2%), injury/trauma (8.5%) repeated pressure (4.1%), medial epicondylitis (2.9%) and benign space occupying lesions (2.9%). Twenty-two patients had expected bilateral lesions whereas 15 had contralateral lesions that were not symptomatic. Eighty-three percent of patients received non-operative first line treatment. Twenty-one percent of these required operative intervention (simple decompression) following further clinical and electrophysiological assessment. Partial or complete recovery occurred in 88%, 80%, 67% and 52% of the arthritis, intra-operative, idiopathic and injury cases respectively (P<
0.05). We conclude lesions of the ulnar nerve at the elbow predominate in males and the majority can be treated non-operatively providing clinical and electrophysiological monitoring is possible. Bilaterality is not uncommon and should be excluded. Lesions due to injury have a worse prognosis than those caused by arthritis of the elbow, direct continuous or repeated pressure or where no aetiological factor exists.