Objective: To study the resected volume (RV) and the resected tumour volume (RTV) in the microscopic examination of the TUR specimen in relation to tumour size, clinical variables and outcome. Materials and methods: This prospectively performed population-based study included all patients in the Southeast Healthcare Region in Sweden with T1 UBC registered in the period 1992-2001, inclusive. RV, RTV and important clinic-pathological variables were studied. All patients had T1 tumours including detrusor muscle at the histopathological examination. Median values for RV and RTV were cutoff points for dichotomisation and 3 cm was the cutoff point for tumour size measured at TUR. Recurrence and progression were analysed using Kaplan-Meier curves with Log-rank test and Cox Proportional Hazards analysis. Results: Out of 211 patients we observed low RV in 112 (53%), low RTV in 113 (54%) and tumour size > 3 cm in 109 (52%). Patients with tumour size > 3 cm and low RV had shorter time to recurrence and progression compared to those with high RV (p = 0.006 and p = 0.087, respectively) and this was also the case when comparing patients with low RTV versus high RTV (p < 0.001 and p = 0.017, respectively). Conclusions: Patients with tumours > 3 cm and low RV or low RTV at TUR for T1 UBC are at higher risk for recurrence or progression, indicating an insufficient TUR. Extensive SLR is particularly important for these patients. RV and RTV might also be used as markers to monitor the quality of the TUR to improve treatment outcome.