Atraumatic isolated musculocutaneous nerve problems are uncommon but have been cited in the literature with increasing frequency since the initial cases discussed in 1978. There appear to be two clinically distinct syndromes involving this nerve--a lesion of the musculocutaneous before its division into the lateral cutaneous nerve, causing a mixed motor and sensory syndrome, and a lesion of the sensory portion, which causes pure sensory findings of the lower radial aspect of the volar forearm. The diagnosis of the more proximal lesion is made by the findings of biceps weakness with no deltoid or other muscle involvement, with the possible exception of the coracobrachialis. There may also be a small area of numbness on the radial aspect of the distal volar forearm, which can be missed unless careful examination is carried out. The lateral cutaneous nerve syndrome is characterized by numbness in the radial half of the volar forearm with some diffuse tenderness over the elbow crease just lateral to the insertion of the biceps tendon. Treatment of the mixed lesion is based on absolute rest for a period of 8-12 weeks. Treatment of the lateral cutaneous nerve syndrome is based on small studies but has included splinting, cortisone injections, and decompression of the nerve.