BACKGROUND: It has long been believed that breastfeeding provides protection against ulcerative colitis and Crohn disease. Studies designated to test this hypothesis were conducted without reaching conclusive results. OBJECTIVE: The aim of this meta-analysis was to examine the role of breastfeeding in preventing inflammatory bowel disease and to summarize the evidence gathered about this subject. DESIGN: A meta-analysis was performed on 17 relevant articles that were found by using MEDLINE, EMBASE, the Internet, and articles' references. The publications were fully reviewed and divided, on the basis of their quality, into 3 groups. RESULTS: Studies showed heterogeneous results. The pooled odds ratios of all the 17 reviewed studies, calculated according to the random-effects model, were 0.67 (95% CI: 0.52, 0.86) for Crohn disease and 0.77 (0.61, 0.96) for ulcerative colitis. However, only 4 studies for Crohn disease and 4 for ulcerative colitis were eventually included in the highest quality group. In this group, the pooled odds ratio was 0.45 (0.26, 0.79) for Crohn disease and 0.56 (0.38, 0.81) for ulcerative colitis. CONCLUSIONS: The results of this meta-analysis support the hypothesis that breastfeeding is associated with lower risks of Crohn disease and ulcerative colitis. However, because only a few studies were graded to be of high quality, we suggest that further research, conducted with good methodology and large sample sizes, should be carried out to strengthen the validity of these observations.