Collecting (Bellini) duct carcinoma of the kidney is a rare lethal tumor, and its prognostic factors remain unclear. The present study investigated the prognostic significance of neutrophil-to-lymphocyte ratio, which has recently been recognized as a readily available prognostic marker in various malignancies, in patients with collecting duct carcinoma. Of 11 patients who were pathologically diagnosed with collecting duct carcinoma at our institution, nine died of collecting duct carcinoma, one died of a postoperative complication, and one was alive, with a median follow-up period of 6 (range: 0-97) months. Both univariate and multivariate analyses associated neutrophil-to-lymphocyte ratio ≥4 (median) with worse cancer-specific survival. Notably, the sole surviving patient maintained a low neutrophil-to-lymphocyte ratio (<4) both at the initial diagnosis and at the time of distant recurrence. These results suggest that neutrophil-to-lymphocyte ratio might serve as a useful biomarker for collecting duct carcinoma as well as other malignancies.