Patient letters provide a permanent record of the genetic counseling that was provided and are unique in medical care; rarely do other health care providers send summaries written specifically to their patients and families. We surveyed genetic counseling training program directors and found that while the acquisition of patient letter-writing skills was considered important, there were no specific guidelines made available to students. To develop letter-writing guidelines, we evaluated patient letters, reviewed references on professional correspondence, surveyed the medical literature, and worked with a writing consultant. The guidelines we subsequently developed and present here include a format for writing patient letters, suggestions on presenting medical information in understandable terms, and wording considerations. These patient letter-writing guidelines are intended to serve as a guide for teaching students this important skill and as a resource for practicing health care professionals.