A 1993 study examined the association between pneumoconiosis and cor pulmonale using a computerized data base of hospital records in Ontario (Hospital Medical Records Institute, HMRI). The present investigation was undertaken to confirm the coding of the diagnoses of a subset of the hospital discharges from that study, to determine the validity of the coding of the diagnoses of coal workers' pneumoconiosis (CWP), and to identify work exposure (occupation and industry) information available in hospital records. We sent abstraction forms to hospitals for 521 subjects who were hospitalized for pneumoconiosis, cor pulmonale, or both conditions, requesting information regarding diagnoses, occupation and industry data, and X-ray results. Abstracts were received for 720 (76%) of 944 discharges that were sought. The hospital abstractions confirmed the HMRI coding for 90% of the charts with these conditions, including 63%, 97%, and 96% discharges for CWP, silicosis, and asbestosis, respectively. Specific dust exposures were indicated in 42% of the charts with a code indicating a diagnosis of CWP, and of these, 67% indicated exposure to coal dust. Of charts with a code indicating a diagnosis of silicosis, 73% with specific dust information indicated silica exposure, and 95% of those for asbestosis indicated exposure to asbestos. Of 34 individuals in this data set known from the Ministry of Labour's Chest Clinic X-ray Surveillance Program of miners to have silicosis, 33 (97%) were diagnosed by the hospitals as having pneumoconiosis, and all but two were silicosis. Hospital records, as reflected by HMRI data, are reliable indicators of cor pulmonale and pneumoconiosis. The agreement with the Chest Clinic's X-ray diagnoses provides additional objective confirmation of the accuracy of the hospital information. There were relatively few cases of silicosis miscoded as CWP. At least for pneumoconioses, hospital records contained information about the exposures that led to these diseases in approximately 50% of the cases. However, whether hospital records would prove useful for detecting other work-related conditions that are not pathognomonic of occupation is not known. The importance of taking occupational histories needs continued emphasis in medical education and training.