The common definition for most health insurance companies for pre-eisting health condition is “having been in treatment by a doctor for a certain period of time before the policy was purchased”.  It could be just any sickness as long as it has an ongoing treatment.   Usually this is any health condition that you have consulted or being in treatment with the doctor for the last 12 months (or so as the policy dictates) before you apply for a health insurance plan. Health insurance companies, generally, do not cover pre-eisting health conditions.  They may either deny coverage for this permanently or after a certain waiting period which may vary from 6 months to 2 years.  If the health insurance company allows its coverage, you will most likely be charged with a higher premium. Regarding your situation of having been diagnosed with a cancer as already a policy holder, health insurance companies may not considered this as a pre-eisting condition since you are not under certain treatment for that condition as well has any knowledge of it prior to the effectivity of the insurance.  However, according to the National Coalition for Cancer Survivorship (NCCS) organization, if you are a cancer survivor you definitely have a pre-eisting condition from the time of diagnosis and for the rest of you life. - June 3, 2009 @ 4:46 pm