The global, randomized, open-label KEYNOTE-185 study closed early after an interim analysis showed an unfavorable benefit-risk profile with pembrolizumab plus lenalidomide and low-dose dexamethasone (Rd) versus Rd alone in treatment-naive, transplant-ineligible multiple myeloma. This subgroup analysis reported outcomes in the Japanese population. Patients were randomly assigned (1:1) to pembrolizumab plus Rd or Rd alone, stratified by age and International Staging System. The primary end point was progression-free survival (PFS). Fifty-two Japanese patients were randomly assigned to pembrolizumab plus Rd (n = 27) or Rd (n = 25). The median follow-up was 7.2 months (range, 0.4-13.8). The median PFS was not reached (NR); 6-month PFS was 91.2% versus 86.2% with pembrolizumab plus Rd versus Rd [hazard ratio (HR), 0.31; 95% CI, 0.06-1.63]. The median overall survival (OS) was NR; 6-month OS was 96.2% versus 95.7% with pembrolizumab plus Rd versus Rd (HR, 0.33; 95% CI, 0.03-3.72). With pembrolizumab plus Rd versus Rd, grade 3-5 adverse events occurred in 70.4% versus 69.6% of patients; serious adverse events occurred in 40.7% versus 52.5%. Although in the Japanese subgroup of KEYNOTE-185 adding pembrolizumab to Rd did not show an unfavorable risk-benefit, the analysis is limited by short follow-up and small sample size, affecting generalizability of the results.