We studied Carpal Tunnel Syndrome prevalence in part time and full time female supermarket cashiers and in a control group (female primary school teachers). Subjects underwent a clinical examination in which information about personal, physiological, pathological and occupational factors were collected by a physician with a questionnaire and a self-administered Katz's hand diagram. The study protocol included median nerve conduction studies (NCS) for each worker, performed bilaterally according to the palmar technique described by J. Kimura. Case definition of Carpal Tunnel Syndrome was based on the combination of typical symptoms (classic/probable or possible) and electrodiagnostic findings according to the Consensus Criteria for the Classification of Carpal Tunnel Syndrome published by Rempel et al. in 1998. Biomechanical risk for upper limb was assessed by a group of trained observer using videotape and scales of hand activity level (HAL) and normalized peak of force (PF) proposed by the American Conference of Governmental Industrial Hygienists (ACGIH): supermarket cashier job tasks resulted on the threshold limit value line, confirming high biomechanical risk factors for CTS. Both symptoms and case prevalence resulted higher in supermarket cashiers than in control group and in full time cashiers if compared with part time ones. This difference between groups of part-/full-time cashiers could be due to total hours of exposure during the week and/or to the amount of recovery time between work sessions. Further longitudinal study could give more information about the role of different biomechanical risk factors in the onset of cumulative trauma disorders of the upper limb.