The presence of anti-heat shock protein 60 (Hsp60) antibodies in healthy individuals and the association of these antibodies with diseases such as arthritis and atherosclerosis are well documented. However, there is limited population-level data on interindividual variation in anti-Hsp60 levels. We investigated the influence of early-life factors on IgG reactivity to human Hsp60 at age 18 years. A population-based prospective birth cohort study included 5914 births in the city of Pelotas, Brazil, in 1982. Early-life exposures were documented during home visits in childhood. In 2000, 79% of all males in the cohort were traced. Sera from a systematic 20% sample (411 subjects) were analyzed. Anti-Hsp60 total IgG reactivity was determined by ELISA. Data were analyzed using analysis of variance and generalized linear models. Anti-Hsp60 reactivity was lognormally distributed and showed a significant direct correlation with low birthweight (p=0.039) and total duration of breastfeeding (p=0.018), of which only the latter remained significant after adjustment for potential confounders. Reactivity was not associated with asthma, pneumonia, diarrhea, or early-life malnutrition. Mother-child immunological interactions, rather than infection/disease factors seem to be associated with reactivity to Hsp60 later in life. This is in agreement with the hypothesis that maternal antibodies influence future antibody profile.