A pre-existing condition is any illness, injury, or health condition that existed before your insurance coverage began. In underwritten individual health plans, insurers ask about your medical history and may exclude coverage for pre-existing conditions, charge higher premiums, or decline your application entirely. Guaranteed-issue and conversion plans accept applicants regardless of pre-existing conditions, but some limit coverage for them or apply a waiting period first — it varies by plan, so check the plan's waiting periods. The definition of what counts as pre-existing varies by insurer but generally includes any condition for which you received treatment, consultation, or medication within a specified lookback period — often 12 to 24 months before your coverage start date.