Introduction. The treatment requirements for non-muscle invasive bladder cancer (NMIBC) (Ta, T1) and muscular invasive bladder disease (T2) differ considerably, therefore a correct staging of the disease is most important. The staging of the disease is frequently underestimated during the primary tumour resection. The objective of the study. To evaluate the results of repeated transurethral resections of the bladder tumours, to assess the treatment outcomes. Material and methods. 160 patients diagnosed with NMIBC underwent transurethral resection of the bladder tumours (TUR) and repeated TUR (reTUR). A data analysis was carried out following the interventions, with histopathological examination, disease staging, and dynamic assessment after 1-year follow up. Results. The average age of the patients was 65.7 years (range 28-86 years) and most of the patients were male, 139 (87%). In most of the cases, the tumours were single, less than 3 cm, and of low-grade in 52%. At reTUR, the residual disease was found in 33% (25/76) of cases. Of these patients, 12 were Ta and 7 were T1, while 2 were carcinoma in situ (Tis) with residual T1 and 4 were upstaged to T2 disease. 62% of residual tumours were detected within the initial resection area. The recurrence rate after 1-year follow-up in the group of reTUR vs. TUR group was lower (29% vs. 56%), as well as disease progression (5% vs. 13%), respectively, after the 1-year follow up. Conclusions. Residual tumours commonly occur following a transurethral resection of high-risk non-muscle invasive bladder cancers. The repeated resection procedure helps in diagnosing residual tumours which have been initially assessed as the T1 stage and may improve the treatment outcomes.