OBJECTIVE: To evaluate the association between the cystic fibrosis (CF) genotype and the rate of diabetes complicating pregnancy. METHODS: We conducted a retrospective cohort analysis of all pregnant patients with CF from 1972-2011 at a single institution. Patients who were homozygous for the ΔF508 mutation were compared with patients who were heterozygous for the ΔF508 mutation. Primary outcomes measured were incidence of CF-related diabetes and gestational diabetes mellitus (GDM) stratified by CF genotype. Secondary outcomes measured included pancreatic insufficiency, preterm premature rupture of membranes, preterm delivery, mode of delivery, gestational age at delivery, and maternal mortality. RESULTS: We identified 54 pregnancies among 36 women who met inclusion criteria. Of these pregnancies, 28 (51.9%) were carried by women who were homozygous for the ΔF508 mutation. Homozygous women had a significantly greater incidence of pancreatic insufficiency (89.3% compared with 61.5%, P=.03) and diabetes complicating pregnancy (60.7% compared with 23.1%, P<.01) compared with heterozygous women. In addition, there was some evidence of an increased incidence of GDM specifically among homozygous women (35.7% compared with 15.4%, P=.12). Regarding neonatal outcome, there was a lower mean birthweight (2,881 g compared with 3,203 g, P=.04) among the women who were homozygous for the ΔF508 mutation. There was no statistical difference in preterm deliveries, mode of delivery, gestational age at delivery, rate of preterm premature rupture of membranes, or incidence of maternal mortality between the two groups. CONCLUSION: Women with CF who are homozygous for the ΔF508 mutation have an increased risk of having a pregnancy complicated by diabetes.