The global, randomized, open-label KEYNOTE-183 phase 3 study was closed early after an interim analysis showed unfavorable risk–benefit when pembrolizumab was added to pomalidomide and dexamethasone in patients with relapsed or refractory multiple myeloma (MM). This subgroup analysis reported outcomes in 27 Japanese patients randomly assigned to receive pembrolizumab plus pomalidomide and dexamethasone ( n  = 15) or pomalidomide and dexamethasone alone ( n  = 12). Co-primary endpoints were progression-free survival (PFS) and overall survival (OS). After a median (range) follow-up of 9.6 (1.4–15.3) months in Japanese patients, median PFS 6.5 vs 2.8 months; hazard ratio (HR) 0.16 (95% CI 0.03–0.83) and OS not reached vs 14.8 months; HR 0.46 (95% CI 0.05–4.20) seemed to favor the pembrolizumab plus pomalidomide and dexamethasone arm. Objective response rate was numerically higher in this group (47%) than in the pomalidomide and dexamethasone group (25%). The safety profile was consistent with that of the overall study population. No deaths were attributed to a study drug by the investigators. Although adding pembrolizumab to pomalidomide and dexamethasone did not show unfavorable risk–benefit in the Japanese subgroup of KEYNOTE-183, the analysis is limited by short follow-up and small sample size, which affects the generalizability of the results.