To determine, for Veterans Health Administration (VA) enrollees who lived and were hospitalized in New York State between 1998 and 2000, the primary payers for their non-VA admissions, whether the primary payer mix varied by condition treated, and whether the Medicare claims data that VA acquired on its Medicare-enrolled patients captured all or most of their non-VA inpatient care. Using VA and New York State administrative and clinical databases, we conducted a retrospective study examining 75,046 residents of New York State who were enrolled in the VA and had 159,843 inpatient admissions in New York hospitals not in the VA system. For each admission, we determined the major diagnostic category, the primary payer for the admission, and whether the patient was Medicare-enrolled. Our analyses separated veterans into those younger than age 65 and those ages 65 or older. The payer mix for younger veterans' non-VA admissions varied considerably by major diagnostic category. Among veterans who also were Medicare enrollees, Medicare did not pay for 10% of the non-VA hospitalizations of older patients or 20% of those for younger patients. Using only Medicare claims data may significantly underestimate VA patients' reliance on non-VA inpatient care. To better inform planners about VA's service market and diagnosis-specific service utilization patterns across VA and non-VA providers, VA should work with states to develop comprehensive inpatient datasets.