Abstract Objectives To investigate the risk of adverse outcomes following discordant antibiotic treatment (urinary organism resistant) for culture-confirmed community-onset lower urinary tract infection (UTI). Methods Cohort study using routinely collected linked primary care, secondary care and microbiology data from patients with culture-confirmed community-onset lower UTI (COLUTI). Antibiotic treatment within ±3 days was considered concordant if the urinary organism was sensitive and discordant if resistant. The primary outcome was the proportion of patients experiencing urinary infection-related hospital admission (UHA) within 30 days. Secondary outcomes were the proportion of patients experiencing reconsultation within 30 days, and the odds of UHA and reconsultation following discordant treatment, adjusting for sex, age, risk factors for complicated UTI, previous antibiotic treatment, recurrent UTI and comorbidities. Results A total of 11 963 UTI episodes in 8324 patients were included, and 1686 episodes (14.1%, 95% CI 13.5%–14.7%) were discordant. UHA occurred in 212/10 277 concordant episodes (2.1%, 95% CI 1.8%–2.4%) and 88/1686 discordant episodes (5.2%, 95% CI 4.2%–6.4%). Reconsultation occurred in 3961 concordant (38.5%, 95% CI 37.6%–39.5%) and 1472 discordant episodes (87.3%, 95% CI 85.6%–88.8%). Discordant treatment compared with concordant was associated with increased odds of UHA (adjusted OR 2.31, 95% CI 1.77–3.0, P < 0.001) and reconsultation (adjusted OR 11.25, 95% CI 9.66–13.11, P < 0.001) on multivariable analysis. Chronic kidney disease and diabetes mellitus were also independently associated with increased odds of UHA. Conclusions One in seven COLUTI episodes in primary care were treated with discordant antibiotics. In higher risk patients requiring urine culture, empirical antibiotic choice optimization could meaningfully reduce adverse outcomes.