You might be surprised to discover that cancer doesn't rank number one. By Cameron Huddleston, Former Online Editor May 5, 2010 When it comes to setting life-insurance rates, insurers want to know how healthy you are to determine how much of a risk you'll be to insure. Having a health problem doesn't necessarily mean your rate will be outrageous, but you likely will pay higher premiums than your healthy peers. How much more you'll pay depends on your condition. Insure.com has put together a list of the top five most expensive medical conditions when you're buying life insurance. If you have one of these conditions, see Get the Best Rates on Life Insurance for tips so you won't pay more than you have to. 1. Heart disease. This condition will affect life-insurance rates most. Even having a family history of heart disease can force you to pay a higher premium. 2. Diabetes. People with Type I diabetes that developed during childhood will have higher rates -- and sometimes trouble finding a company that will insure them. People with adult-onset diabetes who can manage their condition through medication or diet have lower rates. Advertisement 3. Cancer. The type you have, the severity and treatment received affect your premiums. For example, an external sun-related lesion may have little or no impact on your rate. See Getting Life Insurance After Cancer for more information. 4. Obesity. Because obesity and several other health conditions go hand in hand, insurers take your weight into consideration. However, weight ranges to qualify for the best rates vary from company to company. 5. Pulmonary disease. Expect to pay a higher premium for life insurance if you have had life-long asthma (not seasonal asthma).