Several instruments have been proposed to improve treatment decisions in elderly cancer patients, but evidence of their impact in clinical practice is limited. The aim of this study was to analyze the role of clinical and functional factors in predicting serious adverse events, including death, severe toxicity or treatment interruption, during chemotherapy in elderly cancer patients. The survey evaluated elderly with lung or colon or breast cancer treated with chemotherapy, followed by S. Giovanni Battista Hospital. We enrolled 110 consecutive patients older than 70 years of age with lung (n=45), colon (n=50) and breast (n=15) cancer between October 2004 and October 2005. Overall, 73/110 patients (66.4%) experienced adverse events as death (n=14), grades III and IV toxicity (n=40), or treatment interruption for other reasons (n=19). The variables with stronger predictivity were advanced stage, toxicity of treatment, level of comorbidity and Karnofsky performance status (KPS). instrumental activities of daily living (IADL) index and age itself were not independent predictors. In conclusion our results confirm the need of a careful selection of elderly patients suitable for chemotherapy, giving more weight to comorbidity and KPS scores than to age itself. The potential role of other functional evaluations need to be further assessed in randomized controlled trials.