Background: In a randomized, double-blind, placebo-controlled trial (J-FORCE), we previously reported the efficacy of olanzapine (OLZ) 5 mg plus triplet antiemetic therapy for cisplatin (CDDP)-based chemotherapy-induced nausea and vomiting (CINV) in the delayed phase (24–120 h after CDDP treatment). Here, we report the results of a pre-planned subgroup analysis of this trial (in which risk factors were used as the allocation factors). This analysis was designed to determine which patients benefit more from OLZ. Methods: Subgroup analysis was performed on complete response (CR: no emesis and no rescue medication) in the acute (within 24 h of CDDP treatment) and delayed phase and time to treatment failure (TTF: time from CDDP treatment to the first vomiting or use of rescue medication). Data from 705 patients in the efficacy analysis population (354 in the OLZ group and 351 in the placebo (PLA) group) were analyzed by sex (male/female), age (≥55 years/ < 55 years), and CDDP dose (≥70 mg/m²/ < 70 mg/m²). For CR, we calculated point estimates of differences between groups and 95% confidence intervals and performed a Mantel-Haenszel test. We used the Kaplan-Meier method for the analysis of TTF, and comparisons between groups were made using a log-rank test. Results: Delayed CR (OLZ versus PLA) and risk difference (RD) of delayed CR following OLZ treatment were significantly greater than following PLA in the following subgroups: male (83.1% versus 70.5%, RD 12.6%, p = 0.001), female (70.9% versus 56.4%, RD 14.5%, p = 0.021), age ≥55 years (78.7% versus 67.6%, RD 11.1%, p = 0.003), age < 55 years (81.0% versus 57.4%, RD 23.6%, p = 0.005), and CDDP ≥70 mg/m² (78.8% versus 65.3%, RD 13.5%, p < 0.001). TTF of all subgroups (male/female, ≥55 years/ < 55 years, and ≥70 mg/m²/ < 70 mg/m²) was significantly longer in the OLZ group than in the PLA group (HR 0.493, p < 0.001; HR 0.612, p = 0.022; HR 0.586, p < 0.001; HR 0.401, p = 0.005; HR 0.546, p < 0.001; HR 0.543, p = 0.031, respectively). Conclusions: Our results suggest a benefit of OLZ 5 mg plus triplet therapy regardless of risk factors for CDDP-based CINV. Clinical trial information: UMIN000024676.