You’re worried that you have cancer or another serious condition. Maybe you have been having trouble breathing, and you think it’s lung cancer. Maybe you have a suspicious spot on your face that could be skin cancer.

Regardless, you go in and see your doctor. They check you out and tell you that nothing is really wrong. Maybe they diagnose it as something else; they tell you the spot is just acne, for instance, or that your breathing issues just mean you’re fighting through a cold. You should be fine.

Fast forward a few months, and it turns out you do have cancer. The doctor did not catch it fast enough, and now it’s far more serious than it would have been if you had gotten treatment when you first came in.

How often does something like this happen? How often are doctors wrong?

While every doctor is an individual and may have a higher or lower mistake rate, some studies have suggested that about one out of every five people who do come down with a serious condition get misdiagnosed at least once before the truth is discovered. That’s 20% of the total. So, while it doesn’t happen to everyone, it is very common.

Common or not, these types of mistakes can have serious ramifications. What if your lung cancer has progressed to the point that it can only be treated, not cured? What if your skin cancer has spread to other parts of the body? That delay could really cost you and could even prove fatal. From a legal standpoint, be sure you know exactly where you stand.