Background <p>Accurate estimation of the Peritoneal Cancer Index (PCI) is essential for selecting patients with peritoneal metastases who may benefit from cytoreductive surgery (CRS). Although cross-sectional imaging is routinely used for preoperative staging, its ability to reflect intraoperative tumor burden remains imperfect. Diagnostic laparoscopy may provide additional information in selected cases.</p> Methods <p>We conducted a retrospective cohort study of patients who underwent CRS for peritoneal metastases at a tertiary cancer center between August 2023 and February 2025. Radiologic PCI (rPCI) was compared with intraoperative PCI assessed during open surgery (crsPCI). In patients who underwent diagnostic laparoscopy, laparoscopic PCI (lapPCI) was also compared with crsPCI. Agreement between methods was evaluated using correlation and concordance analyses.</p> Results <p>Fifty-six patients were included in the radiologic analysis, and 16 underwent diagnostic laparoscopy before CRS. Radiologic PCI demonstrated good agreement with intraoperative PCI but tended to underestimate the extent of peritoneal disease. Laparoscopic PCI showed closer agreement with surgical PCI than radiologic assessment. However, the laparoscopic subgroup was small and predominantly composed of patients with gastric cancer, limiting the generalizability of these findings.</p> Conclusions <p>In this selected surgical cohort, radiologic PCI provided a reasonable estimate of intraoperative tumor burden but consistently underestimated disease extent. Diagnostic laparoscopy appeared to improve concordance with surgical PCI and may offer complementary staging information in selected high-risk or borderline cases, particularly when imaging findings are equivocal. Given the limited size and selected nature of the laparoscopic subgroup, these results should be interpreted cautiously and viewed as supportive rather than definitive evidence for the routine use of laparoscopy across all tumor types.</p>