Symptoms associated with upper extremity cumulative trauma disorders (UECTDs) recently have been reported in professional sign language interpreters. The present investigation is a case control study of potential biomechanical factors that may exacerbate or maintain UECTD-related symptoms in this occupational group. Based on the results of a medical screening, interpreters were classified into two groups: working with pain (n = 16) and working without pain (n = 13). There were no significant differences between the groups on age, gender, years signing, years interpreting, and wrist and forearm endurance and flexibility as measured during an isokinetic strength test of the upper extremities. Subjects were exposed to a standard interpreting task. Groups were compared on measures of repetitiveness of hand/wrist motion, work/rest cycle, postural stress, and smoothness of movement. Heart rate, pain, fatigue, and perceived reduction in extremity flexibility also were measured. The group working with pain demonstrated a distinct pattern of potential biomechanical risk factors previously associated with UECTDs in other occupations. By comparison with the control group, those working with pain exhibited fewer rest breaks, more frequent hand/wrist deviations from neutral, more frequent lateral excursions from an optimal work envelope, and more rapid finger/hand movements while interpreting. Significant group differences on self-report measures of pain, fatigue, and perceived limitation in range of motion also were observed. An analysis of heart-rate response to the interpreting task revealed that both groups demonstrated a modest increase in heart rate to the interpreting task, although interpreters working with pain displayed lower heart rates across all phases of the experimental task.(ABSTRACT TRUNCATED AT 250 WORDS)