BACKGROUND: Newborn screening for cystic fibrosis (CF) in Illinois uses an immunoreactive trypsinogen/DNA methodology; most false-positive results identify unaffected carriers. METHODS: Parents whose child received a negative result from the sweat test after a positive newborn screening for CF were surveyed >/= 6 weeks later by telephone. All parents received genetic counseling while waiting for the sweat-test results. RESULTS: A total of 90 parents participated. Overall knowledge of CF was high (78%), but the ability to understand the CF screening results was mixed. Although 94% of the parents understood that their child did not have CF, only 79% (62 of 78) of participants whose child had a mutation knew their child was definitely a carrier, and only 1 of 12 parents whose child had no mutation understood that the child may be a carrier. Respondents stated that most relatives were not interested in genetic testing. Both parents had been tested in only 13 couples. Fewer than half (36 of 77 [47%]) of the untested couples expressed interest in genetic testing. Although most participants were satisfied with the process, parents expressed frustration because of the lack of prospective newborn screening discussions by prenatal and pediatric providers and lack of knowledge and sensitivity by those who initially notified them of the abnormal newborn screening results. Speaking to a genetic counselor when scheduling the sweat test decreased anxiety for many parents (53 of 73 [73%] were "very worried" at notification versus 18 of 73 [25%] after scheduling; P < .001). CONCLUSIONS: Parental knowledge about CF is high, but confusion about the child's carrier status and the concept of residual risk persist despite genetic counseling. Relatives express low interest in carrier testing.