Most older Australians have at least one chronic health condition. The management of chronic disease is associated with potentially severe economic consequences for patients and their households, partially due to the financial burden associated with out-of-pocket costs for medical and health-related care. A questionnaire was mailed to a cross-sectional sample of older Australians in mid-2009, with 4574 responding. Multivariate logistic regression models were developed to investigate the relationships between multimorbidity and out-of-pocket spending on medical and health-related expenses, including the factors associated with severe financial stress among older Australians. We found a positive relationship between number of chronic conditions and out-of-pocket spending on health and that people with multiple chronic conditions tend to be on lower incomes. People with five or more chronic conditions spent on average five times as much on their health as those with no diagnosed chronic conditions and each additional chronic disease added 46% to the likelihood of a person facing a severe financial burden due to health costs.