BACKGROUND:: Health services use typically is examined using either self-reports or administrative data, but the concordance between the 2 is not well established. OBJECTIVE:: We evaluated the concordance of hospital and physician utilization data from self-reports and claims data, and identified factors associated with disagreement. METHODS:: We performed a secondary analysis on linked observational and administrative data. A national sample of 4310 respondents who were 70 years old or older at their baseline interviews was used. Self-reported and Medicare claims-based hospital episodes and physician visits for 12 months before baseline were examined. Kappa statistics were used to evaluate concordance, and multivariable multinomial logistic regression was used to identify factors associated with overreporting (self-reports > claims), underreporting (self-reports < claims), and concordant-reporting (self-reports ĝ̂1/4 claims). RESULTS:: The concordance of hospital episodes was high (° ≤ 0.767 for the 2 - 2 comparison of none vs. some and ° ≤ 0.671 for the 6 - 6 comparison of none, 1, ĝ€■, 4, or 5 or more), but concordance for physician visits was low (° ≤ 0.255 for the 2 - 2 comparison of none versus some and ° ≤ 0.351 for the 14 - 14 comparison of none, 1, ..., 12, and 13 or more). Multivariable multinomial logistic regression indicated that over-, under-, and concordant-reporting of hospital episodes was significantly associated with gender, alcohol consumption, arthritis, cancer, heart disease, psychologic problems, lower body functional limitations, self-rated health, and depressive symptoms. Over-, under-, and concordant-reporting of physician visits were significantly associated with age, gender, race, living alone, veteran status, private health insurance, arthritis, cancer, diabetes, hypertension, heart disease, lower body functional limitations, and poor memory. CONCLUSIONS:: Concordance between self-reported and claims-based hospital episodes was high, but concordance for physician visits was low. Factors significantly associated with bidirectional (over- and underreporting) and unidirectional (over- or underreporting) error patterns were detected. Therefore, caution is advised when drawing conclusions based on just one physician visit data source. Copyright © 2007 by Lippincott Williams and Wilkins.