I have an overweight friend who thinks shes thinner than she is, how do i honestly tell her shes seriously overweight and needs help for her health?

Be a real friend: A real friend tells people the truth but does it tactfully. Put it in this form... List several things you like about the person. Ask her, "how do you know you have lost weight?" if she claims she is weighing herself, don't argue. You cannot assume responsibility for another adult's life, and relationships are more important than being right.

Friendly advice: Why do you feel that you need to tell her? I appreciate your concern as a friend, but her health is her concern. Like her for who she is. If she is having untreated health problems that are having a negative impact on her life, than encourage her to see a doctor.