Seventy-four patients were operated at Bichat hospital for chronic ulnar nerve entrapment at the elbow between 1982 and 1988. For 62 of them, the etiology of the compression was idiopathic and these cases were treated by neurolysis only or, if the nerve was unstable, by neurolysis associated with medial epicondylectomy. For 12 of them, the etiology of the compression was post-traumatic and these cases were treated by anterior subcutaneous transposition of the nerve using a fat sling. The average follow-up is 28 months and the results take into account the clinical preoperative grading according Mac Gowan's classification: grade I subjective symptoms combined with hypoesthesia in ulnar fingers grade II: weakness and wasting of the interossei combined with subjective symptoms, grade III: marked weakness and wasting of the interossei, adductor pollicis, and hypothenar muscles combined with anesthesia in ulnar fingers. The 62 idiopathic compressions treated by neurolysis only or, if the nerve was unstable, by neurolysis associated with medial epicondylectomy showed 51 very good and good results. The 12 post-traumatic compressions treated by anterior subcutaneous transposition of the nerve using a fat sling showed 9 very good and good results. The authors stress the importance of their approach which takes account of the clinical preoperative grading and the etiology of the compression in order to apply correct surgical treatment.