I've blogged about this before, but I've decided to make an annual habit of it. It can't be repeated too often. Genealogy can save your life. It would have saved mine if I hadn't already known what I needed to know.
The American Cancer Society recommends the 'average' person to start getting checked for Colon cancer at age 50. However, for those with a history of the disease in the immediate family, they recommend to start the tests ten years prior to the earliest it has been diagnosed. My maternal grandmother died at age 51. So I was prepared to start getting tested at age 40. Then a close kin, slightly older, had their test, and polyps were discovered and removed. So last year, at age 39, I decided there wasn't any good reason to wait on ceremony, and my doctor agreed. I had my first colonoscopy, and 2 polyps were removed, one of which was pre-malignant. If I had waited until I was 50, there's a chance I wouldn't have made it. Since I knew to check early, the polyps were caught before they could become dangerous, and hopefully any future polyps will also be caught beforehand.
[Note: As I understand it, the causal connection between polyps and cancer actually isn't conclusive. Scientists haven't proven that pre-malignant polyps always become malignant, or that polyps always lead to cancer. Nor that everyone who gets cancer had pre-malignant polyps at one time that could have been detected. But they know enough to remove the polyps when they see them.]
Other diseases have genetic predispositions. So it is important to know the medical histories of your parents, grandparents, and where possible, your great grandparents. The primary method of doing this, for those who are deceased, is to find their death certificates. It is rare to find any prior to 1900, but for those who lived into the 20th century, especially those who lived past 1920, finding death certificates, while not always easy, isn't usually difficult - if you know when and where they died.
1) Local Courthouses
Most counties in America house archives of their Vital Records (birth, marriage, death.) A few have strict restrictions on who can request copies, limiting them to 'immediate family' which may not include grandchildren.
2) State Archives
State archives often have copies of the county records, with fewer restrictions on access.
3) Online Databases
Some counties and states have begun putting their records online. Ancestry, FamilySearch, and Footnote also have some databases available to search.
4) Funeral Homes
Funeral homes often retain their own copy of the death certificate, and their copy may differ slightly from that held by the County or State. It may contain details about where in a cemetery plot the individual was buried, or details about the funeral itself. If you don't know the funeral home, search in archives of local newspapers and try to find an obituary, as obituary notices often include this information. The funeral home copy may also be at times the only copy you have access to if the county and state are too restrictive.
Once you have found the death certificate, if you don't recognize instantly the words written under 'cause of death' conduct an internet search on them at Google or Yahoo. My family history made identifying "Carc. of Col." as "Carcinoma of Colon" fairly easy, though I suspect some might have stumbled over the abbreviation. Several ancestors were diagnosed with "Interstitial Nephritis." I'd never heard of this before, but it is a kidney ailment often caused by a reaction to pain medication. Unfortunately, the death certificates didn't indicate the cause of the original pain.