Shamus over at TwentySided (check it out, his DM of the Rings is lolful) was side-tracked from a medieval RPG by maunderings about the medieval mortality rate.
"Women cranked out babies at an alarming pace, yet the population remained flat. Run those numbers in your head and it becomes clear that people who lived to adulthood where a small minority of the total number of people born. Their lives were bleak, harsh, and filled with death. They died of things that are trivial to fix today. I wouldn’t have made it. Asthma would have killed me. If that didn’t get me, the infection I had at 20 would have done the job."
He mentions that asthma would have killed him young without medical treatment. I would have died at 5 or 6 when I had my appendix out. Plus, Even if I'd made it, I would have been almost functionally blind and half-deaf. How many on my flist, I wonder, would have made it to their present age if they had lived medievally?
Shamus puts it, "How about you? How long would you have lived in the middle ages? Ignore all the general risks - like typhoid or the plague or cholera - that everyone would have faced in general. Let’s assume you were lucky and missed those. (Unless by some chance you actually DID face one of them in your life.) Also ignore the fact that your deadly injury might have been caused by modern technology, like an auto accident. Just pretend you were trampled by a horse or something. So, given the injuries and illness you’ve faced in your life so far: Did you make it? Would you have survived to your current age?"