Background: Given the paucity of relevant data, this study estimates the cost of intellectual disability (ID) to families and the government in Australia. Method: Family costs were collected via the Client Service Receipt Inventory, recording information relating to service use and personal expense as a consequence of ID. Government expenditure on the provision of support and services was estimated using top-down costing. Results: A total of 109 parents participated. The cost of ID in Australia is high, especially for families. Total economic costs of ID are close to $14,720 billion annually. Opportunity cost of lost time provided 85% of family expense. A comparison of family expense and social welfare benefits received suggests that families suffer considerable loss. This may impact on families' physical and emotional wellbeing. Conclusions: Monitoring of changes in expenditure is required. Policies should ensure that money devoted to ID is allocated in a rational, equitable, and cost-effective manner. (Contains 2 tables.)