Oh, that is one of the hardest things to do. What helped me was going to the school counselor with some of my friends and asking them to help me tell her about it. By law (at least, over here) they have to tell your 'rents if you're hurting yourself. Of course, if you think it would be better if they heard it from you, you should do like the others are saying on here and break it to them really slowly. Just start out: "Mom, Dad, I have something to tell you. I need you to promise me that you won't react and you won't say anything until I'm done. And also, please try and keep an open mind and look at this from my perspective." After they've promised, tell them about your cutting and then explain your reasons to them. It is also imperative that you point out that you aren't doing this for attention, but because you need an escape. (That is, I hope, your reason, right?) I hope for your sake that they are more understanding and helpful than my mother was (she never told my father). Good luck!