While a number of high-profile cases of Medicare fraud—costing hundreds of millions of dollars each—have been reported in the media, there is speculation that a lot of the fraudulent activity that occurs within the health care system is actually the result of innocent or ignorant mistakes on the part of providers. If you think you're safe because you've never intentionally committed fraud, or you think investigations and audits aren't costly, you may need to brush up billing compliance—preferably before you code another file or sign another claim form.