Filing a bankruptcy will make your credit score drop. However, in many cases it is likely that you are already behind on credit cards or medical bills and your credit score has already taken a hit. The good thing about a bankruptcy is that your credit score will begin to rebound after your case is filed.
A Chapter 7 bankruptcy will report on your credit for 10 years. A Chapter 13 bankruptcy will report for 7 years. This does not mean that you are doomed to have bad credit that entire time. Most of my clients find that their credit score has improved dramatically after only 2-3 years from the file date.
I have posted a couple links below for articles on how to rebuild your credit after filing bankruptcy.