*4.1. Step 1: Consensus Definition of Complexity*

Reports on morbidity or mortality of TURBT were researched in the PubMed database (English language, 4/2009–4/2019, key words: "transurethral resection (of) bladder", "morbidity", "complication" "mortality" or "death"). A senior author (BM) reviewed all abstracts and analysed the articles of potential relevance before proposing to the panel a working definition of complexity in TURBT (Table S1).
