Ulnar neuropathies following surgery are common. However, they often go undetected during the early postoperative period, because the patient may be unaware of symptoms related to the neuropathy. Nerve conduction studies are useful in localizing the lesion, but are usually employed only in cases developing signs and symptoms. We undertook this study to determine the incidence, time of onset, and outcome of clinical and subclinical ulnar neuropathies. Electrophysiological studies were carried out preoperatively, immediately following surgery, and 4 to 6 weeks postoperatively in 20 coronary artery bypass patients. Conduction velocity across the elbow was reduced in 3 limbs (8%) postoperatively, all of which were detected immediately following surgery. One patient developed conduction block and weakness in ulnar supplied intrinsic hand muscles. Denervation was seen in 2 cases and, in 1 case (5%), a right brachial plexus injury was clinically evident 5 days following surgery. All newly developing ulnar neuropathies were asymptomatic, with most recovering to their preoperative electrophysiological status at follow-up.