Breast-feeding has been suggested to have a protective effect against the development of type 1 diabetes. In the present study, we investigated the relation between duration of breast-feeding and β-cell autoantibodies in 5-year-old non-diabetic children who participated in a prospective population-based follow-up study (the All Babies in Southeast Sweden study). Autoantibodies to insulin (IAA), glutamic acid decarboxylase (GADA) and the protein tyrosine phosphatase-like IA-2 (IA-2A) were measured by radiobinding assays. A short duration of total breast-feeding was associated with an increased risk of GADA and/or IAA above the ninety-fifth percentile at 5 years of age (OR 2·09, 95 % CI 1·45, 3·02; P < 0·000) as well as with an increased risk of IAA above the ninety-fifth percentile at this age (OR 2·89, 95 % CI 1·81, 4·62; P < 0·000). A short duration of exclusive breast-feeding was associated with an increased risk of GADA, IAA and/or IA-2A above the ninety-ninth percentile (OR 2·01, 95 % CI 1·08, 3·73; P = 0·028) as well as with an increased risk of IA-2A above the ninety-ninth percentile (OR 3·50, 95 % CI 1·38, 8·92; P = 0·009) at 5 years of age. An early introduction of formula was associated with an increased risk of GADA, IAA and/or IA-2A above the ninety-ninth percentile (OR 1·84, 95 % CI 1·01, 3·37; P = 0·047) at 5 years of age. The positive association between a short duration of both total and exclusive breast-feeding, as well as an early introduction of formula, and positivity for β-cell autoantibodies in children from the general population suggests that breast-feeding modifies the risk of β-cell autoimmunity, even years after finishing breast-feeding