Résumé : Introduction: Intravesical instillations of BCG represent an established treatment of high-risk non-muscle-invasive bladder cancer but also carry considerable toxicity. The aim of this work was to identify adverse effects, their impact on the treatment and the possible involvement of the BCG strain used. Material and methods: To evaluate adverse events in terms of incidence, severity and moment of occurrence, we performed a retrospective analysis of all patients treated with BCG in our institution from 1998 to 2012. Results: One hundred and forty-six patients were retained for analysis, 140 (95.9%) finished their first induction cycle. Thirty patients (20.6%) had to stop the treatment because of BCG-related adverse events, 80% of which happened during the first 3 BCG cycles (12 instillations). The strain used may have had a significant impact: 16 out of 42 patients (38.1%) treated with Connaught (Immucyst®) and 14 out of 104 patients (13.5%) treated with Tice (Oncotice®) had to stop treatment because of BCG related adverse events (P = 0.0019) with an odds ratio of 2.83 (IC 95%: 1.52-5.23). Conclusion: BCG-related adverse events generally occur at the beginning of the treatment and therefore do not limit the use of BCG maintenance therapy. Good instillation practice and, in our series, the shift from Connaught to Tice strain enabled to significantly reduce BCG-related adverse events through time. The potential implication of the BCG strain used should be evaluated in prospective trials. Level of evidence: 4.