To explore the prognostic importance of metastatic volume in a contemporary daily practice cohort of patients with newly diagnosed metastatic hormone-naive prostate cancer (mHNPC) and to develop a pragmatic prognostic model to predict survival for these patients. Since 2014, 113 patients with newly diagnosed mHNPC were prospectively registered. Statistical analysis was performed using SPSS 25.0™ with two-sided p value < 0.05 indicating statistical significance. Univariate and multivariate cox regression analyses were performed to identify prognostic risk factors. Kaplan-Meier method with log-rank statistics was constructed to analyze difference in survival in the prognostic groups. Model performance was assessed using the Concordance-index (C-index) and cross-validated in R v3.4.1. High-volume mHNPC (HVD) was defined as the presence of visceral metastasis or ≥ 4 bone metastases with ≥ 1 appendicular lesion. Multivariate analysis identified HVD (p = 0.047) and elevated alkaline phosphatase (ALP) (p = 0.018) as independent prognostic risk factors for overall survival (OS). Consequently, three prognostic groups were created: a good (no risk factors), intermediate (1 risk factor) and poor prognosis group (2 risk factors). Median OS for the good, intermediate and poor prognosis group was not reached, 73 and 20 months (95% CI 9-31 months with p < 0.001 and Correspondence-index of 0.78), respectively. We developed a pragmatic and qualitative prognostic model consisting of three prognostic risk groups for OS in a daily practice cohort of patients with newly diagnosed mHNPC. Independent prognostic risk factors included in the model were HVD and abnormal ALP.