© Photographer: Scrappinstacy | Agency: Dreamstime Some conditions can make it difficult for you to find health insurance.

"Pre-existing condition" is a phrase that can make both health insurance companies and those applying for insurance cringe. Simply defined, a pre-existing condition is a health condition or illness that you have had before your first day of coverage on a new plan. This rather broad definition is just the tip of the iceberg, and the actual health coverage for those with pre-existing conditions depends on a few factors -- including the type of health insurance plan, the level of care needed for your pre-existing condition, and your health insurance history.

Because a person with a pre-existing condition can cost an insurance company millions, it is in their best interest to exclude those who have them. In this article, we'll explain the many aspects of a health insurance plan's pre-existing conditions exclusion.

It is important to note that different rules apply for individual health insurance plans and group plans set up by your employer. We'll start by discussing group plans and then get into individual plans, which are generally much stricter about pre-existing conditions.

The Pre-Existing Conditions Exclusion
Now we've defined pre-existing conditions, the question remains: How is a condition like this going to affect my health care coverage? There is no simple answer. Some conditions will not affect your coverage at all, but others could keep you from having coverage for that condition for up to a year. When an insurance company applies a pre-existing condition exclusion, it can limit or exclude coverage for that condition.

In a group health plan, some situations may seem to fit the pre-existing condition definition, but exclusions don't apply to them. For example, if you have a gene that makes you more likely to get Huntington's disease -- but you don't actually have Huntington's disease -- that usually isn't considered a pre-existing condition.

Many HMOs have an affiliation period that you must wait out before your coverage kicks in. The affilation period can't be longer than two months from your enrollment date, or three months for late enrollees. But HMOs can't use both affiliation periods and pre-existing condition exclusions -- it's one or the other.

While the idea of a pre-existing condition exclusion period can be daunting to those in need of health care, there are rules and regulations that can work in your favor. In the next section, we'll explain the limitations of the affiliation period -- and how you may be able to eliminate it altogether.