The influence of breastfeeding on blood pressure in later life is uncertain. The authors conducted a systematic review of published studies from which estimates of a mean difference (standard error) in blood pressure between breastfed and bottle-fed subjects could be derived. They searched MEDLINE and Excerpta Medica (EMBASE) bibliographic databases, which was supplemented by manual searches of reference lists. Fifteen studies (17 observations) including 17,503 subjects were summarized. Systolic blood pressure was lower in breastfed compared with bottle-fed infants (pooled difference: –1.4 mmHg, 95% confidence interval (CI): –2.2, –0.6), but evidence of heterogeneity between study estimates was evident (χ216 = 42.0, p < 0.001). A lesser effect of breastfeeding on systolic blood pressure was observed in larger (n ≥ 1,000) studies (–0.6 mmHg, 95% CI: –1.2, 0.02) compared with smaller (n < 1,000) studies (–2.3 mmHg, 95% CI: –3.7, –0.9) (p for difference in pooled estimates = 0.02). A small reduction in diastolic blood pressure was associated with breastfeeding (pooled difference: –0.5 mmHg, 95% CI: –0.9, –0.04), which was independent of study size. If causal, the small reduction in blood pressure associated with breastfeeding could confer important benefits on cardiovascular health at a population level. Understanding the mechanism underlying this association may provide insights into pathways linking early life exposures with health in adulthood.