Gynaecological oncology treatment yields no fewer complications and side effects than those met in any other oncology field. Patients and clinicians are highly alerted by the ominous diagnosis and sometimes seek for high risk, experimental, or even unproven therapies and are consequently prepared to accept high complication rates that would otherwise be unacceptable. Still, risk reduction remains a high priority. This is achieved by appropriate risk assessment, risk-to-benefit ratio balancing, treatment individualisation, close follow up through all treatment stages, and prompt patient informing and participation in decision making. The chapter aims to summarize the main complications of surgery, chemotherapy, and radiotherapy as well as the main ways to overcome them.