Im not Dr Taylor, but I have run a marathon. However, although I do have CF I dont know what my pfts are. I am lucky enough that I am in very good health and I guess its because I have a mild case of CF. I therefore tend to compare myself, in terms of my health and fitness, to my friends and other athletes who dont have cf, and not to others who do have cf.Having said this I think the best advice is not to jump straight in to a marathon. Maybe start by entering a 10k race (about 1/4 marathon) and then maybe enter a half marathon after. Once you complete a half marathon you will have a good idea if you are able to take on the full thing. It is possible though, so believe in yourself. Take it slow and let me know how you are getting on!Rob 24 wcf