The goal of this study was to determine if the effectiveness of first-line maintenance therapy with niraparib differs among patients with newly diagnosed advanced ovarian cancer based on the timing of surgery and the presence or absence of postoperative residual disease. Response to first-line platinum-based chemotherapy for newly diagnosed advanced primary ovarian, primary peritoneal, or fallopian tube cancer with niraparib: a post hoc analysis from the phase 3 PRIMA/ENGOT-OV26/GOG-3012 (NCT02655016) research. In the intention-to-treat population, progression-free survival (PFS) was analyzed according to surgical status (primary versus neoadjuvant chemotherapy/interval debulking surgery [PDS versus NACT versus IDS]) and postoperative residual disease status (no visible versus visible residual disease [NVRD versus VRD]). Before enrolling in PRIMA (N = 733), 236 patients underwent PDS (32.2%), while 481 patients (65.6%) received NACT/IDS. The median progression-free survival (PFS) (niraparib versus placebo) and hazard ratios (95% CI) for progression were identical in the PDS (13.7 vs 8.2 months; HR, 0.67 [0.47-0.96]) and NACT/IDS (14.2 vs 8.2 months; HR, 0.57 [0.44-0.73]) subgroups, respectively. The hazard ratio (95% CI) for progression in NVRD patients who were given NACT/IDS (n = 304) was 0.65. (0.46–0.91). The hazard ratios (95% CI) for progression in individuals with VRD after PDS (n = 183) and NACT/IDS (n = 149) were 0.58 (0.39-0.86) and 0.41 (0.27-0.62), respectively. Due to a small sample size (n = 37), PFS could not be calculated for those with PDS and NVRD. Overall, PDS and NACT/IDS subgroups showed similar responses to niraparib in this post hoc analysis. The greatest benefit from maintenance niraparib treatment was shown in patients with NACT/IDS and VRD.