Objective: The purposes of this study were: (1) to determine whether breast-fed infants with tongue-tie have decreased rates of breast-feeding at 1 week and 1 month of age, (2) to determine the prevalence of tongue-tie, and (3) to test the usefulness of the Assessment Tool for Lingual Frenulum Function (ATLFF) in assessing the severity of tongue-tie in breast-feeding newborns. Methods: A case-control design was used. All infants in the Regions Hospital newborn nursery were examined for tongue-tie. Tongue-tied babies were examined using the ATLFF. Two breast-feeding babies with normal tongues were identified and matched for each case. Mothers were interviewed when the babies were 1 week and 1 month old. Results: The prevalence of tongue-tie was 4.2%. Forty-nine tongue-tied and 98 control infants were enrolled. Tongue-tied babies were 3 times as likely as control babies to be bottle fed only at 1 week [risk ratio (RR), 3.11; 95% confidence interval (CI), 1.21, 8.03) By 1 month, tongue-tied babies were as likely as controls to be bottle fed only. (RR, 1.00; 95% CI, 0.55,1.82) Twelve of the tongue-tied infants had ATLFF scores of "Perfect," none had scores of "Acceptable," and 6 had scores of "Function Impaired." The remaining 31 infants had scores that fell into none of these categories. Conclusions: Tongue-tie is a relatively common condition in newborns. Affected infants are significantly more likely to be exclusively bottle-fed by 1 week of age. The ATLFF was not a useful tool to identify which tongue-tied infants are at risk for breast-feeding problems.