Many cancer patients experience psychological suffering during their journey from diagnosis, through treatment, to survivorship or the end of life. Their psychological distress can become severe enough to interfere with their ability to cope with cancer. Conditions such as anxiety, depression, insomnia, and delirium often occur among cancer patients. Although distress is prevalent in cancer patients, it is often under-recognized and under-treated in the oncology setting. Psychological distress may have a negative effect on patients' quality of life. The prevention, early detection, and proper management of distress are important for improving patients' quality of life during and after cancer treatment. It is therefore necessary to develop a system for assessing and managing distress. The US National Comprehensive Cancer Network developed guidelines for distress management in 1999. Korean recommendations for distress management were released in 2009. The Korean government recently designated integrated supportive care centers for survivors at the National Cancer Center and regional cancer centers. The supportive care service is provided for cancer survivors who have completed first-line anti-cancer treatment. Psycho-oncology is one of the most important components of supportive care in cancer. Distress management yields many benefits for cancer patients, but the reality is that significantly distressed patients are often not properly referred for psychosocial care. All distressed patients should be properly referred for psychosocial care, and the psychosocial care of cancer patients should be integrated into routine cancer care practice.