Suboptimal bowel preparation can result in missed colorectal adenoma that can evolve into interval colorectal cancer. This study aims to identify the predictive factors associated with missed adenoma on repeat colonoscopy in patients with suboptimal bowel preparation at initial colonoscopy. A total of 441 patients with suboptimal bowel preparation on initial colonoscopy and who had repeat colonoscopy within two years were included from 2007 to 2014 in six tertiary hospitals. Suboptimal bowel preparation was defined as ‘poor’ according to the Aronchick scale or a score ≤ 1 in at least one segment or total score < 6 according to the Boston bowel preparation scale. Of 441 patients, mean age at initial colonoscopy was 59.1 years, and 69.2% patients were male. The mean interval from initial to repeat colonoscopy was 14.1 months. The per-patient adenoma miss rate (AMR) was 42.4% for any adenoma and 5.4% for advanced adenoma. When the association between baseline clinical characteristics and missed lesions on repeat colonoscopy was analyzed, dyslipidemia (odds ratio [OR], 5.19; 95% confidence interval [CI], 1.14–23.66; P = 0.034), and high-risk adenoma (OR, 4.45; 95% CI, 1.12–17.68; P = 0.034) on initial colonoscopy were independent risk factors for missed advanced adenoma. In patients with suboptimal bowel preparation, dyslipidemia and high-risk adenoma on initial colonoscopy were independently predictive of missed advanced adenoma on repeat colonoscopy.