Hospital billing is complex and opportunities for fraud and gaming vary considerably by payment methodology. Cost-plus billing rewarded hospitals for having high overhead and inflating costs. Per diem systems encourage long lengths of stay and low complexity caseloads. DRG systems often have problems with upcoding (reporting a diagnosis or complication that increases payment). The lesson is that any payment system needs checks and balances. Healthcare providers must be held accountable for performance, but that, too, opens new opportunities for gaming.