This is used mostly in health plans people buy on their own. It is how far back a health insurance company will look at their health records. If the period is 5 years, people must list all conditions they had or were treated for in the last 5 years. If the list is wrong or has certain health problems on it, the company can say no. They can also say yes and call for a pre-existing condition waiting period. This is the time someone must wait before the condition will be covered. Disability plans also have look-back periods. They may exclude benefits for disabilities caused by pre-existing conditions.