Background: Limited studies have estimated the prevalence of ulnar neuropathy (UN) in the workplace. Hand diagrams have been demonstrated to have a good sensitivity and specificity when attempting to identify patients with UN. Objective: To determine the prevalence and associated risk factors for UN among active workers based on results of a hand diagram, and to determine the reliability of hand diagram scoring. Design: Cross-sectional study. Setting: Seven different industrial and clerical work sites. Methods: A total of 501 active workers were screened. Subjects completed a hand diagram and the Job Content Questionnaire, and had ergonomic assessment of their job. Each hand diagram was scored independently by 2 raters. Main Outcome Measures: Rating of the hand diagram for UN. Results: Interrater reliability of scoring the hand diagram for UN was very high. The estimated prevalence of UN was 3.6%. Suspected UN was associated with positioning of the elbow but not by contact stress at the elbow or force at the hand. Smokers had a lower prevalence, but smokers with suspected UN had higher-pack year histories. Workers with suspected UN had a greater sense of job insecurity and lower job satisfaction rating. Conclusions: Hand diagram rating has a high interrater reliability. Suspected UN has a relatively high prevalence among active workers in comparison to prior estimates of the prevalence of UN among the general population and is not strongly associated with ergonomic factors.