BACKGROUND: The aim of this study was to identify the predictive factors for progression defined as any event that shifted the management of the disease from a bladder sparing approach, by comparing patients with pure versus non-pure carcinoma in situ (CIS) of the bladder. METHODS: A retrospective analysis was carried out in consecutive patients affected by newly-diagnosed pure CIS and non-pure CIS (excluding cases with concomitant muscle invasive cancer). All patients were enrolled a in our institution from 1998 to 2010. Data was prospectively collected. Main end point was progression-free survival. RESULTS: Overall, 149 patients with CIS were identified for the analysis. A total of 98 patients had pure CIS (66%). Median follow-up was 103 months (range: 40-206 months). Progression occurred in 29 patients (19%). A total of 30 patients died during the follow-up (20%). In 13 cases (9%), the death was cancer specific. Progression-free survival estimate was 181 months (95% CI: 169-193 months) and 154 months (95% CI: 133-176 months) respectively for pure and non-pure CIS population (P=0.03). Among examined variables (age, gender, symptoms, smoking habit, ASA score, number of bacillus Calmette-Guérin [BCG] instillations), multivariate analysis disclosed that only CIS type was an independent predictor of progression (P=0.03) with a relative risk of 0.37 in favor of pure CIS. CONCLUSIONS: Pure and non-pure CIS are efficiently treated by BCG therapy combined with trans-urethral resection and/or radical cystectomy, with relatively low rate of progression. CIS type was the only significant predictor of progression.