Purpose: Cytoreductive surgery (CRS) +/- hyperthermic intraperitoneal chemotherapy (HIPEC) is a potentially curative treatment for peritoneal malignancy. Diaphragmatic involvement is common and may require peritoneal stripping or diaphragm excision. This study aimed to describe the incidence of post-operative pulmonary complications (PPCs) and assess whether prophylactic chest drains mitigate these complications in a unit that routinely avoids chest drain placement, even when the pleural cavity is entered. Methodology: A retrospective analysis was conducted of patients undergoing CRS +/- HIPEC at Waikato Hospital from 2008-2025. Patients were grouped based on whether diaphragmatic surgery was performed. PPCs were graded using a modified Clavien-Dindo system; with Grade >/= III defined as severe. Statistical analysis was performed using chi-square and Fisher’s exact test. Results: A total of 265 patients were included. PPCs occurred in 88 patients (33%). Patients undergoing diaphragmatic surgery (n=118, 45%) had a higher incidence of PPCs than those without diaphragmatic surgery (48% vs 21%, p<0.001). Severe PPCs (Clavien-Dindo >/= III) occurred exclusively in the diaphragmatic surgery group (16%). Pleural effusions and pneumonia were the most common complications. 8 patients (7%) received prophylactic chest drains at the index operation, all within the diaphragmatic surgery group. Thirteen patients (11%) had pleural cavity entry without prophylactic chest drain placement. There was no significant difference in PPC rates between those with and without prophylactic chest drains (75% vs 42%, p =0.145). 10 patients received therapeutic chest drains (8%). Conclusions: Diaphragmatic involvement during CRS +/- HIPEC is a risk factor for PPCs. Routine prophylactic chest drain placement may not significantly reduce the development of these complications; however, this finding is limited by a low event rate. Further research is needed to clarify the role of prophylactic chest drains in this context.