The company I work for was bought out, the new company offers a SELF-insured health plan that the employer pays out the claims. I know that it is through Aetna as the administator of the plan and it is a POS plan. Can anyone tell me the way a self-insured plan works and what are the drawbacks? I am worried that I am not going to have the coverage I did with my current HMO plan.

Well, you're going to have to compare the coverages! Even the self insured plan should have a sheet to show you what they are covering, at what rate.

The biggest drawback is, of course, that they aren't an insurance company - so that if you have a massive claim (chemo treatments, for example, or a preemie newborn) there isn't any guarantee that the money will be there to pay it. MOST employers have a "stop gap" type plan in place, where an insurance company would pick up all claims over, say, $100,000.

The biggest bonus to it, is they aren't limited by state law in what they can cover. Or what they have to cover. And if the company is a large company, they've probably calculated that it will save them a lot of money to do it this way, which means you'll likely have more broad coverage.

Self-insured plans are exactly that - they are funded by your employer. Since it is a point of service plan (POS) you will have more flexibility than you did with your HMO. With your HMO you have to use the provider that you have chosen within the network and you can be very limited. With a POS you can go to any Dr that you want at any time and have any service done (of course you will have to pay for copays and coinsurance). There are drawbacks if your employer is small and suddenly stops funding the plan - but if you work for a reputable company this shouldn't be a problem.
I would much rather have a POS plan than an HMO - I think you will see the benefits as well.

Honestly, MOST group health plans are now self-funded. The potential exists for your benefits to be as rich as before, potentially more. Check the plan documents, are your copays more or less? How much do you pay a month? Does the new plan cover the same services? Office visits, outpatient surgery, inpatient hospital, pharmacy, physical therapy, mental health, home health, medical equipment??? Check it out.

Fundamentally, the only real difference is this.... Your new company doesn't have to follow state laws regarding health insurance coverage. The old company does.

I am sure they will have a comparable plan. Most self insured companies have a company like Aetna administer it. They also have "Stop-Gap" insurance for any catastrophic illnesses (usually over $100,000).