Metastatic burden is a critical factor for therapy decision-making in metastatic hormone-sensitive prostate cancer. This 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. The 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, while 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.