Use of antibiotics affects the composition of the microbiome and might affect development of colorectal polyps, which are precursors to colorectal cancer.We performed a nested case-control study in Sweden of 45,744 patients with a colorectal polyp (cases) in the nationwide gastrointestinal ESPRESSO histopathology cohort, using unaffected full siblings as controls (n=93,307). Polyps were classified by morphology SnoMed codes into conventional adenomas and serrated polyps. Through linkage to the Prescribed Drug Register, we assessed use and cumulative dispensations of antibiotic until one year prior to polyp diagnosis for cases and their sibling controls.During a median study period of 6.9 years, compared with non-users, users of antibiotics (28,884 cases [63.1%] and 53,222 sibling controls [57.0%]) had a higher risk of colorectal polyps. Risk increased with higher number of dispensations (odds ratio [OR] for ≥ 6 dispensations, 1.33; 95% CI, 1.25-1.43) (Ptrend0.10). We found stronger associations for younger (<50 years) vs older adults (≥50 years) for users of quinolones, sulfonamides, trimethoprim, and cephalosporins (Pinteraction<0.001).In a nationwide case-control study in Sweden, after accounting for hereditary and early life environmental factors, antibiotic use was associated with increased risk of colorectal polyps. Our findings indicate a role for intestinal dysbiosis in early stages of colorectal carcinogenesis.