['To investigate the prognostic value of protocadherin 17 (PCDH17) promoter methylation in serum-derived DNA of patients with bladder cancer.', 'DNA was isolated from serum of patients with bladder cancer and from age- and sex-matched controls. Methylation-specific polymerase chain reaction was used to examine the methylation status of the PCDH17 promoter. The correlations between methylation status and clinicopathological characteristics and overall survival were examined.', 'PCDH17 promoter methylation was detected in 79/151 (52.3%) of patients with bladder cancer, and none of the 43 control subjects. Methylation was significantly associated with larger tumour diameter (>3\u2009cm), high grade (G3) and advanced stage (T2-T4). Patients with PCDH17 promoter methylation had significantly shorter overall survival than those with unmethylated PCDH17 promoter. Methylation was an independent predictor of overall survival.'] Is protocadherin-17 promoter methylation in serum-derived DNA associated with poor prognosis of bladder cancer?