Data are sparse on the incidence of carpal tunnel syndrome (CTS) in the general population, and estimates from workplace settings vary widely among workers' compensation, OSHA logs of recordable illnesses, and other administrative data sources. The reasons that some people with work-related CTS do not file compensation claims are believed to include factors as varied as access to medical care and information about work-related morbidity, employers' medical management and return-to-work programs, and workers' perceived job security and expected success in filing compensation claims. This pilot study was designed to determine the feasibility of using data from a large health maintenance organization (HMO) to estimate the incidence of carpal tunnel syndrome from a relatively well-defined sample of the Massachusetts general population and to estimate the proportion of those incident cases that are likely work-related. Using a retrospective, dynamic cohort study design, computerized files and medical records were used to identify and characterize probable CTS cases. The incidence density rate of diagnosed CTS in this HMO population was estimated as 4.34 cases per 1,000 person years. Agreement was good (82% overall) between medical diagnoses and record reviews. A number of study instruments were developed for this investigation. Four algorithms for searching the HMO medical record database were developed and compared for their utility in locating CTS cases, and final selection has been made for future use. The standardized interview was finalized and evaluated during the course of ten interviews, and a list of revisions for future use has been noted. The decision rules for determination of probability of CTS and of work-relatedness were also revised and evaluated. Data entry templates were developed and utilized for both the chart reviews and case interviews. Several logistical delays impeded the performance of two intended data collection activities. Time did not permit either interviews of cases' employers, or review of workers' compensation records from the state Department of Industrial Accidents. Nevertheless, the primary objective of the project has been fulfilled. Data from this HMO have proved a feasible and effective means of identifying incident CTS cases within a well-defined sample of the general population. In addition, the procedures and decision rules necessary for identification of likely work-related cases have been developed. Although only a small number of cases was evaluated in this pilot study, a future large-scale investigation using the same study methods will likely be able to achieve the substantive goals that motivated this project. Information about etiologically relevant occupational exposures was obtained from a structured interview and scored as to probability of work-relatedness. Among eleven CTS cases interviewed, five (45%) were judged to be definitely or probably work-related.