BACKGROUND: Older patients with metastatic castration-resistant prostate cancer (mCRPC) may be more prone to chemotherapy-induced hematological toxicity, but tailored docetaxel dosing guidelines in older patients are lacking because of conflicting data. OBJECTIVE: This study aims to evaluate the impact of older age on the incidence of hematological toxicity in patients with mCRPC treated with docetaxel in daily clinical practice. METHODS: This study included patients with mCRPC treated with docetaxel between January 2006 and January 2016 at the Netherlands Cancer Institute and Medical Center Slotervaart for whom dosing and hematological toxicity data were available from electronic patient records. We evaluated the impact of age on the incidence of grade 3 and 4 hematological toxicity. RESULTS: In total, 175 patients treated with docetaxel were included in the analysis, with a median age of 67 years (range 47-86). Baseline hematological laboratory values were not age related. After the first treatment cycle, hematological toxicity occurred significantly more frequently in the oldest age quartile (25%, p = 0.02) than in the younger age quartiles (9%, 11%, and 7%, respectively, for age quartiles 1, 2, and 3). CONCLUSION: The risk of hematological toxicity was significantly higher in the oldest age quartile than in younger patients with mCRPC treated with docetaxel in daily clinical practice.