Extra-abdominal spread of pseudomyxoma peritonei (PMP) is a rare event, but extension of the tumor beyond the abdomen into the pleural cavity has been reported. We report a case with synchronous pleural manifestation of PMP confirmed during abdominal cytoreductive surgery that was managed by simultaneous bicavitary hyperthermic chemoperfusion. To the best of our knowledge, this is the first report of bicavitary hyperthermic chemoperfusion for PMP. During the abdominal cytoreductive surgery in a patient with known history of PMP, extensive disease under the right hemidiaphragm was noted, requiring partial diaphragmatic resection. Once the pleural space was entered, separate mucinous deposits on the pleural surface of the diaphragm and lung surface were observed. The involved portion of the right hemidiaphragm and lung were resected. The diaphragmatic defect was left open during the hyperthermic chemoperfusion to treat both the pleural and peritoneal surfaces. The patient's postoperative course was uneventful. Simultaneous bicavitary hyperthermic chemoperfusion is a potential therapeutic option for patients with pleural extension identified during cytoreductive surgery.