AIM: The main objective of the present study was to examine the quality of life of older adults with cancer and investigate factors associated with it. Some practical problems experienced by older adults with cancer are introduced, such as changes in work situation, availability of caregivers and financial difficulties relative to medical expenditures. METHODS: A total of 339 patients aged 65 years or older who were treated for five major cancer diseases--colorectal, stomach, lung, liver or kidney cancer--participated in the present study. The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire was used to measure the quality of life. Performance status (physical functioning) was assigned according to the Eastern Cooperative Oncology Group classification. The Life Orientation Test-Revised was used to assess future expectations. The multiple linear regression analysis was used to identify predictors of the quality of life of older persons with cancer. RESULTS: The results showed that physical functioning and optimism were significant predictors of all four functions (physical, role, emotional and social function) and global quality of life of older adults with cancer. Nearly 60% experienced changes in work situation and had financial burden on medical costs. CONCLUSIONS: The findings suggest that efforts to assess physical functioning with more attention and enhance optimism should be emphasized in interventions for older adults with cancer.