Serrated polyps (SPs) with synchronous advanced adenoma (AA) may increase the incidence of colorectal cancer. However, current studies do not address this combination of SPs and AAs in detail with regard to their clinical characteristics in different age groups. The aim was to assess clinical characteristics and risk factors for SPs with synchronous AA in different age groups.Retrospective cohort study.Electronic medical record data from January 2011 to January 2022 at three grade III class A hospitals were enrolled in the study.A total of 1605 patients with SPs with synchronous AA, including 484 patients in the elderly group and 1121 patients in the non-elderly group, were studied.The elderly group and the non-elderly group.Sex, smoking history, drinking history, body mass index (BMI), SP location, size, morphology and pathology.The incidence of hyperplastic polyps (HPs) with synchronous AA in the elderly group was higher than that in the non-elderly group, while the incidence of sessile serrated adenomas/polyps (SSAs/Ps) with synchronous AA in the non-elderly group was higher than that in the elderly group. Male sex, drinking history and HP size (≤20 mm) were independent risk factors for HPs with synchronous AA in the non-elderly group, while drinking history and HP size (≤15 mm) were independent risk factors in the elderly group. For SSAs/Ps with synchronous AA, male sex, smoking history, drinking history, and SSA size (≥16 mm) were independent risk factors in the non-elderly group; high BMI was an independent risk factor in the elderly group.SPs with synchronous AA showed different clinical characteristics and risk factors in different age groups.© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.