Background: Pleural recurrence after cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) is rare and poorly delineated. Specifically, data are limited on the effect that diaphragmatic peritoneal stripping versus full-thickness resection has on the nature of ipsilateral pleural recurrence and postoperative morbidity. Methods: Patients with peritoneal carcinomatosis who underwent CRS/HIPEC were included from a prospectively maintained database. The patients were divided into three cohorts based on surgical management of the diaphragm as follows: diaphragm-stripping (DS) cohort, full-thickness resection (FTR) cohort, and no diaphragm manipulation (ND) cohort. Postoperative morbidity and incidence of ipsilateral pleural recurrence were evaluated. All diaphragmatic defects were closed before abdominal chemoperfusion. Results: The inclusion criteria were met by 409 CRS/HIPEC procedures: 66 in DS, 122 in FTR, and 238 in ND. Ipsilateral pleural recurrence rates did not differ significantly between the three cohorts (DS 6%, FTR 3%, ND 3%; p = 0.470). Postoperative respiratory complications and overall morbidity were significantly greater for the patients who underwent diaphragmatic disruption (stripping and/or resection) than for the patients who did not (p ≤ 0.0001), but the two groups did not differ in terms of 30-day mortality. However, comparison of FTR with DS showed no impact on major morbidity or pleural recurrence. Conclusion: Although patients undergoing surgical manipulation of the diaphragm during CRS/HIPEC experienced significantly greater morbidity, diaphragmatic stripping did not differ from full-thickness resection in terms of grades 3 and 4 complications or incidence of ipsilateral pleural recurrences. When deemed necessary to achieve complete cytoreduction, full-thickness diaphragmatic resection should be undertaken. In addition, the data support the observation that definitive repair of the diaphragmatic defect before abdominal chemoperfusion does not adversely influence ipsilateral pleural recurrence.