i don't know about Delta F508 being most severe mutation... it is indeed most common. i'm a double delta f508 myself as well. i'm definitely going to discuss the severity of that mutation with my doctor, next time i'm there - week and a half. the only thing i have to say is that if that's the most severe mutation, the cf population is doing good <img src="i/expressions/face-icon-small-smile.gif" border="0"> because as i experienced that, i only started having lung problems at the age of seven, was in a very stabilized condition up until i was 17 and may i add, it was a brilliant condition, i even got a remark once from a PFT's technician - "are you certain you got cf with those pft's?" - and since then, although things went downhill, i'm still doing good and leading a very normal life, with schooling, friends, parties, dates and relationships and sex, and whatever can be found in a life of a twenty [almost 21] year old. basically, it's like everybody says - just take the best care of cf. doing all the treatments, taking all the meds and exercising is the key to good condition.