Inconsistent results regarding the association between red and processed meat intake and the risk of colorectal adenoma (CRA), the precursor of colorectal cancer (CRC), have been reported. To provide a quantitative assessment of this association, we summarized the evidence from observational studies. Relevant studies were identified in MEDLINE and EMBASE until December 31, 2011. Summary relative risks (SRRs) with 95% confidence intervals (CIs) were pooled with a random-effects model. Between-study heterogeneity was assessed using the Cochran's Q and I2 statistics. A total of 21 studies (16 case–control studies and five cohort/nested case–control studies) were included in this meta-analysis. The SRRs of CRA were 1.36 (95% CI = 1.17–1.58) for every 100 g/day increase in red meat intake, and 1.24 (95% CI = 1.12–1.36) for the highest versus the lowest level of red meat intake. Nonlinear dose-response meta-analysis indicated that CRA risk increased approximately linearly with increasing intake of red meat up to ∼ 90 g/day, where the curve reached its plateau. Subgrouped analyses revealed that the increased risk of CRA with intake of red meat was independent of geographic locations, design and confounders. The SRRs of CRA was 1.28 (95% CI = 1.03–1.60) for per 50 g/day increase in processed meat intake, and 1.17 (95% CI = 1.08–1.26) for the highest versus the lowest level of processed meat intake. Increased intake of red and processed meat is associated with significantly increased risk of CRA.