"Out-of-pocket" spending by families supporting an adult family member with mental retardation or related developmental disability was characterized and estimated. Annualized nonreimbursed spending among a sample of 99 Chicago-area households was evaluated through survey and telephone interview across 10 categories of routine daily living expenses and disabilities-related services. The average annual out-of-pocket cost was $6,348. Average pre-tax income for the sample households was $37,657. Although wealthier households reported higher levels of spending, the percentage of household income represented by out-of-pocket costs increased significantly as family incomes decreased. Results were discussed in the context of families as a focus for service planning and public policy and the importance of the family to the nation's system of care.