On November 12, 1997, the National Institute for Occupational Safety and Health (NIOSH) received a request for a Health Hazard Evaluation (HHE) from the management of the Dental Services Branch of the Indian Health Service (IHS) to evaluate work-related musculoskeletal disorders (WRMDs), particularly neck disorders. These managers were concerned that older rear delivery equipment, used by the Branch, was contributing to an increase of WRMDs among employees of the dental clinics. To assess job tasks, the manner in which dental equipment was used, and the WRMDs among the dental personnel, site visits were conducted at 3 IHS clinics on February 9-11, 1998, and 3 more on November 2-7, 1998, by a NIOSH ergonomist and epidemiologist. The ergonomic evaluation included videotaping of tasks, still photographs and observations of job tasks of dentists and dental assistants. The medical evaluation consisted of interviews with employees and a self-administered questionnaire. The questionnaire dealt with work practices, hobbies, and back and upper extremity musculoskeletal problems. The ergonomic evaluation showed that the most significant work risk factors for dentists was static loading of the neck (prolonged focus on small areas inside the patientís oral cavity) and static loading and awkward postures of the hands (anesthetic injection and drilling of patientís teeth) while performing dental tasks. The most significant work risk factors for dental assistants was twisting and turning of the back, and extended reaches of the arms to access dental instruments from the dental trays, which were located behind the patient in 5 of 6 sites. In addition, dental assistants were at risk for hand and wrist disorders possibly from prolonged static postures, forceful exertions of the hands while using dental instruments, and from carving fillings. All employees present on the day of the site visit were eligible for participation in the study and 47 dental workers completed the questionnaire including: 3 at the Colorado River Indian Tribes [CRIT], 11 at the White Mountain Apache Tribes [WMAT], and 6 at the San Carlos Service Unit [SCSU] during the first site visit of February 9-11, 1998, and 11 at Crownpoint, New Mexico, 4 at Winslow, Arizona, and 12 at Tuba City, Arizona during the second site visit of November 3-5, 1998. For our analysis, an upper extremity musculoskeletal disorder was considered to be related to the workplace (WRMD) if this disorder (pain, numbness, tingling, aching, stiffness, or burning in the affected part) occurred within the preceding year and all of the following applied: (1) musculoskeletal disorders began after starting the current job (2) musculoskeletal disorders lasted for more than one week or occurred at least once a month within the past year (3) musculoskeletal disorders were reported as "moderate" (the midpoint) or worse on a five point intensity scale. The prevalence of WRMDs was 48% (21 out of 44 workers) for the neck, 42% (18 of 43) workers for the back and 37% (16 of 43 workers) for the shoulder. Non-dentists had a significantly greater prevalence of work-related [WR] neck musculoskeletal disorders than dentists; nineteen of 30 non-dentists, which included assistants and hygienists, reported WR neck musculoskeletal disorders (63%) while only one of 12 (8%) dentists reported WR neck musculoskeletal disorders (OR 19.0, 95% CI 2.1-859.1). Non-dentists also had a greater prevalence of WR hand/wrist disorders than dentists. Forty-two percent of non-dentists and no dentists reported hand/wrist WRMDs (p=0.007, OR undefined). Workers in the older clinics reported more musculoskeletal disorders than workers in the newer clinics, with the exception of WR back pain where the prevalence was the same in both groups. On the basis of this evaluation, NIOSH investigators concluded that being a dental assistant with the Indian Health Service is associated with a higher prevalence of work-related musculoskeletal disorders than being a dentist. This work-related injury was associated with older clinics, not being a dentist, hand scaling, and malfunctioning dental equipment. Changes that the Indian Health Service should make to prevent and control these disorders are given in the Recommendations section.