Metastatic burden is a critical factor for therapy decision‐making in metastatic hormone‐sensitive prostate cancer. The present study aimed to identify prognostic factors in men with high‐ or low‐metastatic burden treated with primary androgen‐deprivation therapy. The study included 2450 men with de novo metastatic prostate cancer who were treated with primary androgen‐deprivation therapy at 30 institutions across Japan between 2008 and 2017. We investigated the prognostic value of various clinicopathological parameters for progression‐free survival (PFS) and overall survival (OS) in patients stratified by low‐ or high‐metastatic burden. Among the 2450 men, 841 (34.3%) and 1609 (65.7%) were classified as having low‐ and high‐metastatic burden, respectively. Median PFS of the low‐ and high‐burden groups were 44.5 and 16.1 months, respectively, and the median OS was 103.2 and 62.7 months, respectively. Percentage of biopsy‐positive core, biopsy Gleason grade group, T‐stage, and N‐stage were identified to be differentially prognostic. M1a was associated with worse PFS than was M1b in the low‐burden group, whereas lung metastasis was associated with better PFS and OS than was M1b in the high‐burden group. Differential prognostic factors were identified for patients with low‐ and high‐burden metastatic prostate cancer. These results may assist in decision‐making to select the optimal therapeutic strategies for patients with different metastatic burdens. This study investigated prognostic factors according to metastatic burden, and found that prognostic impact of some factors was different. This finding may be valuable in decision‐making to select the optimal therapeutic strategies for patients with different metastatic burdens.