This final report points out that the Indian Health Service (IHS) had not established the controls necessary to ensure that amounts billed to private health insurance companies for medical services were accurate and covered all allowable services. As a result, we estimate that IHS underbilled private insurers by $7.3 million for the 3-month period ending March 31, 1993. In addition, the IHS did not contact private health insurance companies or otherwise follow up on an estimated $1.2 million of unpaid claims. To maximize collections, we recommended that the IHS establish the necessary internal controls, assign adequate resources to its business offices, provide additional training to business office staff to ensure that claims for all covered services are filed and accurate, and implement complete and timely follow-up procedures. The Public Health Service concurred with our findings and recommendations.