The aim of this study was to survey cystic fibrosis (CF) patients to determine the frequency of breast-feeding and its association with onset and severity of CF symptoms. Three thousand, two hundred questionnaires were sent to 30 accredited CF centers for anonymous completion. Eight hundred and sixty-three questionnaires were returned and scanned into a database. All results were adjusted for age at time of filling out the questionnaire. Age at onset of symptoms, percent forced expired volume in 1 sec (FEV1%) predicted, and intravenous (IV) antibiotic use were analyzed based on breast-feeding history. Approximately 49% of respondents received human breast milk at some time, but only 18% were exclusively breast-fed. Breast-feeding exclusively for greater than 6 months was associated with a decrease in disease severity based on recent intravenous antibiotic use compared to no breast-feeding (P = 0.03). There was no statistically significant change in onset of symptoms in the setting of breast-feeding; however, a trend toward delayed onset was seen in those receiving human milk. Fifty-three percent of those who breast-fed exclusively > or = 6 months had FEV1% values > 90%, compared to 47% of those not breast-fed. This is a suggestive but not statistically significant difference. In conclusion, breast-feeding for > or = 6 months is associated with decreased use of intravenous antibiotics in the 2 years prior to administering the questionnaire. This survey indicates that breast-feeding is not harmful to children with CF, and may be beneficial.