OBJECTIVE--To determine the extent of agreement between clinical information recorded on surgery computers of selected general practitioners and similar information in manual records of letters received from hospital consultants and kept in the general practitioners' files. DESIGN--Hospital consultants' letters in the manual records of selected general practitioners were photocopied and the consultants' clinical diagnoses were compared with diagnoses recorded on computer. SETTING--General practices in the United Kingdom using computers provided by VAMP Health for recording clinical information. SUBJECTS--2491 patients who received one of three non-steroidal anti-inflammatory drugs and who attended 58 practices whose computer recorded data were considered after a preliminary review to be of satisfactory quality. RESULTS--Among 1191 patients for whom consultants' letters were forwarded a clinical diagnosis reflecting the diagnosis noted on a consultant letter was present on the computer record for 1038 (87%). CONCLUSION--Clinical information available on the computer records of the general practitioners who participated in this study is satisfactory for many clinical studies.