BACKGROUND AND OBJECTIVES:Using an instrument to measure physical functioning that was normed to the U.S. population, data were obtained from patients with a new diagnosis of breast, colon, lung, and prostate cancer. Two questions were addressed: (a) after controlling for age, and number of comorbid conditions, do site and stage of cancer predict functional limitations prior to diagnosis; (b) using age adjusted national norms on physical functioning, how well do age, number of comorbid conditions, stage, treatment and cluster of symptoms (pain, fatigue, and insomnia) explain changes in physical function between 3 months prior to and 8 weeks following diagnosis? METHODS:Patients 65 years of age and older were accrued from 24 community oncology settings. Consenting patients were interviewed within 8 weeks of initial treatment. The SF-36 was used to measure physical functioning. Comorbidity and symptom experience were assessed through patient report and site and stage of cancer from record audits. RESULTS:Prior to diagnosis of cancer, patients were comparable in physical functioning to the U.S. population aged 55-64, a full decade younger than the sample of cancer patients. Site and stage of disease did not account for variations in physical functioning prior to diagnosis. Compared against national norms, patients with more extensive treatments (surgery plus adjuvant therapy) reported greater loss in functioning. Pain, fatigue, and insomnia had a consistent and significant effect on losses in functioning unrelated to patients' treatments or their comorbid conditions. CONCLUSIONS:Site and stage of cancer prior to diagnosis do not affect functioning. Older cancer patients report higher functioning than their counterparts in the U.S. population. Changes in functioning following diagnosis varied by cancer site. Treatments were related to loss in functioning, but comorbidity was not. Pain, fatigue, and insomnia were significant and independent predictors of change in patient functioning. This underscores the importance of interventions to manage symptoms early in the course of treatment for individuals.