This is a single center, randomized, double-blinded, placebo-controlled Phase 1 clinical study to evaluate the safety and tolerability of up to 3 increasing oral doses of Fenretinide compared to placebo, and to evaluate the pharmacokinetics of Fenretinide in adult CF patients chronically infected with Pseudomonas aeruginosa. A single cohort of 16 clinically stable adult patients will be randomized to either Fenretinide or placebo, in a 3:1 randomization scheme (12 active, 4 placebo).