Imaging studies are crucial in the evaluation of patients with suspected or known peritoneal cancerous dissemination. Despite the major progress that has occurred in radiological technology in the last few years, adequate and early detection of peritoneal surface disease remains a challenge. Improvements in spatial resolution are still insufficient to detect small volume peritoneal implants, often resulting in an underestimation of peritoneal disease burden, as assessed at subsequent surgical exploration. Cytoreductive surgery combined with perioperative intraperitoneal chemotherapy has provided unprecedented results in the management of peritoneal-based neoplasms, provided that a complete (adequate) cytoreduction is achieved. Diagnostic imaging tests are used to select patients who may benefit from this combined treatment by ruling out extraperitoneal involvement and signs of unresectable peritoneal disease. Furthermore, a careful assessment of the disease distribution within the peritoneal cavity, guided by a deep knowledge of the disease's clinical and biological behavior helps in planning the surgical procedure. Close interaction and cooperation between surgeons and radiologists is of utmost importance in this regard, and dedicated, motivated radiologists are required. Contrast-enhanced, multidetector computed tomography scan remains the standard imaging modality in the assessment of peritoneal carcinomatosis. Magnetic resonance imaging may offer complementary valuable data. Positron emission tomography (PET) has a more limited role, its main indication being the detection of unsuspected extraperitoneal involvement in nonmucinous neoplasms.