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ObjectivesTo investigate the risk of upper urinary tract urothelial carcinoma (UTUC) in patients with non-muscle-invasive bladder cancer (NMIBC), in relation to the primary NMIBC tumour risk categories, calendar time trends and intravesical Bacillus Calmette-Guerin (BCG) treatment.Patient and methodsAll patients with primary NMIBC diagnosed 1997-2019 registered in Bladder Cancer Data base Sweden (BladderBaSe) 2.0 were included in the study. Risk of UTUC was calculated by cumulative incidence proportion using competing risk analysis. Associations with risk of UTUC by tumour stage category, calendar time, and intravesical BCG treatment was estimated by hazard ratios from multivariable Cox regression analyses.ResultsOf 36 038 NMIBC patients, 537 (1.5%) were diagnosed with UTUC during a mean time of 7 years in follow-up. The risk of UTUC within 10 years from NMIBC diagnosis was 1.7% (95% 1.6-1.9) with highest estimates for TaG3/CIS. Stage T1 and TaG3/CIS, as compared with TaG1-2 was associated to risk, with stronger associations during later calendar times. Within high-risk NMIBC patients (CIS/TaG3/T1), intravesical BCG treatment was associated with higher risk of UTUC.ConclusionsThis large study of more than 36 000 patients with NMIBC found 1.7% (95% 1.6-1.9) risk of UTUC within 10 years of diagnosis. Differences by tumour stage category indicate the need for refined studies accounting for tumour characteristics, location in the bladder and given treatment to optimise follow-up routines in NMIBC.