States develop specific protocols for cystic fibrosis (CF) newborn screening to reflect the population served. We hypothesized that mutation distribution and detection rates would differ between Hispanic and non-Hispanic CF patients diagnosed by IL newborn screen with more Hispanic infants carrying mutations not detected by the state panel. Data from CF cases diagnosed via newborn screen in IL between 3/1/2008 and 10/31/2010 were reviewed. More Hispanic infants with CF had one or more undefined mutations after screening, in comparison to non-Hispanic Caucasian patients (40% vs. 9.5%; p < 0.002). The risk of having a positive diagnosis of CF with only one mutation noted by positive newborn screen increases 2-fold in Hispanic Caucasian versus non-Hispanic Caucasian infants (5% vs. 2.4%). Health care providers must be aware of the limitations of CF newborn screening to ensure appropriate counseling and prompt referral for a positive newborn screen, even when zero or one mutations are identified.