This article is the first to describe Department of Veterans Affairs (VA) patients' use of Medicaid at a national level. We obtained 1999 national VA enrollment and utilization data, Centers for Medicare and Medicaid Services enrollment and claims, and Medicare information from the VA Information Resource Center. The research team created files for program characteristics and described the VA-Medicaid dually enrolled population, healthcare utilization, and costs. In 1999, VA-Medicaid dual enrollees comprised 10.2% of VA's annual patient load (350,000/3,450,000); 304,000 were veterans. These veterans differed marginally from VA's veteran patients, being on average half a year younger and having 1% fewer males. Dual enrollees with mental health diagnoses and care were almost three times as numerous as long-term care patients; these two groups accounted for ~60% of dual enrollees. Dual enrollees disproportionately included housebound veterans and veterans needing aid and assistance. Half the dual enrollees had 12 months of Medicaid eligibility, and total Federal expenditures per patient not in managed care programs averaged >$18,000 (median >$6,000). Dually enrolled women veterans cost ~55% less than men. Medicaid benefits complement VA and are more accessible in many states. VA researchers need to consider including Medicaid utilization and costs in their studies if they target populations or programs related to long-term care or mental disorders.