 Cystic fibrosis CF related diabetes CFRD and glucose intolerance affects more than 50-75 of teens and adults with CF. The 1998 North American CF Foundation on CFRD categorized the disease differently than other types of diabetes: CFRD with fasting hyperglycemia FH, CFRD without FH and transient CFRD. The outcome of this consensus conference was the use of insulin as the only recommended treatment of CFRD. Although the conference report mandated treatment for CFRD with FH, treatment was not mandated for the other types of CFRD, the choice to treat was left to the clinicians discretion. However, insulin was the only recommended therapy for all types of CFRD. Although some clinicians have used basal bolus regimens as the insulin management, many still use NPH. Given the need for CF patients to eat many frequent meals and snacks to maintain their weight, use of NPH insulin rarely renders good glycemic control. A basal bolus regimen is much more physiologic and would allow good glycemic control even with frequent meals and snacks. To date, there are no studies documenting safety and efficacy of true basal insulin, or a basal bolus regimen. Furthermore, protein catabolism and excessive muscle loss has been well documented in CF patients, both in those with and those without, glucose intolerance. Studies by our group and others have documented that a major reason for the catabolism is resistance to insulins anti-catabolic effects on protein turnover. Thus, there is potential clinical benefit of improving muscle mass and general health by insulin treatment even for CF patients who do not have fasting hyperglycemia. A non-peaking basal insulin would be the only reasonable choice, yet studies are lacking. Our overall goal is to study the safety and efficacy of LevemirTM for the improvement of glycemic control of patients with CFRD. As a second goal, we will explore the ability of this basal insulin to improve protein catabolism and muscle mass. The study will be conducted as a six month trial. 