OBJECTIVE: Comprehensive assessment of perceived concerns can be used to guide supportive care appropriate to individual cancer patients. This study sought to determine the prevalence of cancer patientsʼ concerns and the degree to which these concerns contribute to patientsʼ quality of life. METHODS: Participants were patients with all types of cancer, who completed an Internet survey questionnaire regarding comprehensive concerns about physical, psychological, psychosocial and economic aspects of having cancer. The questionnaire was based on the newly developed Comprehensive Concerns Assessment Tool and the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire. RESULTS: We obtained complete data from 807 patients. Factors related to ‘self-management’ concerns were the most common (61.2%), followed by concerns about ‘psychological symptoms’ (48.5%), ‘medical information’ (46.2%), ‘daily living’ (29.9%), ‘pain’ (17.6%), ‘constipation’ (15.6%) and other ‘physical symptoms’ (15.2%). Multiple regression analysis revealed that all concerns except those about ‘medical information’ significantly contributed to quality of life. CONCLUSIONS: Cancer patientsʼ concerns were shown to be multidimensional and significantly associated with quality of life. Thus, assessment of patientsʼ concerns should be multidimensional in nature, and a multidisciplinary care team should help patients improve their quality of life.