The differences in demographics, anthropometrics, psychosocial profile, medical history, electrophysiologic measures, and ergonomic risks were investigated for workers with and without reported symptoms among all workers who had a confirmed abnormality of the median nerve in one or both wrists. Data were collected as part of a cross sectional study of active workers at six different work sites. These sites included two automobile parts manufacturers, a furniture manufacturer, a spark plug manufacturer, a paper container manufacturer, and an insurance company. The jobs ranged from loading machines and monitoring their operations to highly repetitive hand transfer and assembly operations. Office jobs ranged from incidental use of keyboard to medium use in conjunction with insurance claim processing. Of the 727 workers screened, 184 (25%) had evidence of a median mononeuropathy in at least one hand. Of these, 51% reported symptoms of numbness, tingling, burning, or pain in the wrist, fingers or hand. When stratified by presence or absence of symptoms, the two groups differed in terms of gender distribution, triceps skin folds, high repetition level, finger and wrist posture, hand force, history of diabetes, and level of job insecurity. There was a trend toward a prolonged relative latency of the median compared to the ulnar nerve. Most of the psychological variables did not differ significantly between the two groups. Ergonomic factors related to repetition, fingers and wrist posture, and average force applied differed significantly. The authors conclude that a relatively high number of active workers had prolongation of the median nerve reaction time on cross sectional screening, yet half were asymptomatic. Women were three time more likely than men to report symptoms among workers with a median mononeuropathy. Workers required to use their hands at higher repetition rates were also more likely to report symptoms.