OBJECTIVES:  To determine if and to what extent records obtained from PBM pharmacy claims differ from source documents obtained directly from pharmacy providers.  Also this study sought to explore possible associations between patient, pharmacy benefit, and pharmacy provider characteristics and the likelihood a patient would have missing prescription claims. METHODS: This study used a cross sectional survey of 1,484 patients residing in a single state with a common pharmacy benefit.  Patient profiles describing all prescriptions filled in a pharmacy between January 1, 2002 through June 30, 2002 of these patients were requested  directly from their pharmacy providers.   Logistic regression was used to explore the factors associated with a person receiving a prescription that did not appear on the PBM claims.  RESULTS:  Of the 1484 eligible recipients sampled,  profiles were obtained for 323 (22%) persons and there were analyzable profiles for 315 (21%) persons.  Of  those 2,977 prescriptions filled for the 315 persons, 207 (7.0%) were missing from the claims files indicating that 93% were captured.  Prescription drugs such as iron products, digoxins, diuretics, sulfonylureas, and antigout were more likely to be missing from the PBM claims.   Only prescription volume consistently influenced the likelihood a patient would have a missing prescription from the PBM claims (OR =1.08; 95%CI:1.05-1.12).  CONCLUSIONS: Claims obtained from pharmacy benefit companies capture approximately 93% of prescription records when verified with records obtained from pharmacy providers.  The rate of missing records from PBM claims does not appear to be meaningfully influenced by most finance based pharmacy benefit design features, however, certain drugs available over the counter and less expensive drugs may have less complete claims records compared to other classes of drugs.  Higher prescription utilizers are more likely to have prescription records filled that are not captured by PBMs.