Health services utilization information is important for outcomes research. This study assessed the reliability of self-reports of health services utilization in respiratory patients. Patients reported health services use and other information during three telephone interviews over 6 months. Reports of visits to general practitioners (GPs), specialists, emergency room (ER)/clinics, and hospital admissions were compared with corresponding fee service claims in the Ontario Health Insurance Plan administrative database in 83 subjects. Agreement between the two sources was calculated using observed agreement and estimated kappa. Substantial agreement was found for hospital admissions and visits to respiratory specialists. Agreement was moderate for GP visits and slight for ER/clinic visits. Patient self-report of ER use appeared unreliable and may be related to imprecise questionnaire wording and inadequately defined fee service codes. The findings emphasize the importance of the methods used to assess the reliability of patient self-reports used in outcomes research.