This article describes the sources of financially catastrophic health care expenses among disabled elderly persons. Using a cost-to-income approach and data from the 1981-1982 Channeling Demonstration project, we examined the types of health care costs (hospital, physician and ancillary care, nursing home, and prescription medicine) that contributed to overall expenses. For the Channeling sample, out-of-pocket expenses for prescription medicines and for nursing home care were the principle source of catastrophic expenses.