As a medical provider in private practice if you are going to bill an HMO I recommend that you and your staff retain a billing firm to give instruction as to how to properly bill your services.  Not only will this information keep you out of a billing issue with the HMO, but you will also learn how to legally maximize your billing to capture the highest amount permitted.  You want to avoid a claim of over billing because not only could that claim cost you a very large amount in repayments, but you also might be in an allegation of fraud situation with the Department of Health or the Department of Education.