PURPOSE OF THE STUDY: This paper is a report of a study of the Assistance, Support, and Self-health Initiated through Skill Training (ASSIST) randomized control trial. The aim of this paper is to understand whether participating in ASSIST significantly changed the out-of-pocket (OOP) costs for family caregivers of Alzheimer's disease (AD) or Parkinson's disease (PD) patients. DESIGN AND METHODS: Secondary analysis of randomized control trial data, calculating average treatment effects of the intervention on OOP costs. Enrollment in the ASSIST trial occurred between 2002 and 2007 at 2 sites: Durham, North Carolina, and Birmingham, Alabama. We profile OOP costs for caregivers who participated in the ASSIST study and use 2-part expenditure models to examine the average treatment effect of the intervention on caregiver OOP expenditures. RESULTS: ASSIST-trained AD and PD caregivers reported monthly OOP expenditures that averaged $500-$600. The intervention increased the likelihood of caregivers spending any money OOP by 26 percentage points over usual care, but the intervention did not significantly increase overall OOP costs. IMPLICATIONS: The ASSIST intervention was effective and inexpensive to the caregiver in direct monetary outlays; thus, there are minimal unintended consequences of the trial on caregiver financial well-being.