Objective: To determine the prevalence of aquagenic wrinkling of the palms (AWP) in patients with cystic fibrosis (CF) compared with control patients, and evaluate for genotype-phenotype correlations. Since its first description over 30 years ago, AWP has frequently been anecdotally associated with CF, but this association has not been confirmed in a rigorous prospective casecontrol study. Design: Blinded comparison. Setting: The CF and dermatology clinics at St Louis Children's Hospital. Participants: Forty-four individuals with CF from a CF clinic and 26 controls from a dermatology clinic. Intervention: Participants were tested for AWP using 3 minutes of water immersion with room-temperature tap water. Main Outcome Measure: The degree of AWP was scored from 0 (no wrinkling) to 4 (severe wrinkling) by 3 blinded physicians. For genotype-phenotype correlations, patients with CF were divided into those homozygous for the ΔF508 mutation and those with other genotypes. Results: The mean AWP score of the CF group was significantly higher than the mean score of the control group (1.5 vs 0.6; P<.001). Patients with CF who were homozygous for the ΔF508 mutation (n=27) had significantly higher scores than patients with CF who were not homozygous for the ΔF508 mutation (n=17) (1.7 vs 1.1; P=.02). The 17 patients with CF who were not homozygous for the ΔF508 mutation still had higher scores than the control group (1.1 vs 0.6; P=.03). There was no correlation between sweat chloride concentrations measured at the time of diagnosis and AWP score. Conclusions: Our results confirm the association between AWP and CF. Among patients with CF, greater AWPoccurs in those who are homozygous for the ΔF508 mutation.