A growing literature finds that a significant fraction of American families experience high or "catastrophic" burdens of medical spending. Families facing mental health problems may be especially vulnerable to high burdens. This study uses data from the Medical Expenditure Panel Survey to determine the annual and within-year concentration of medical spending and the extent to which mental health treatment contributes to high out-of-pocket burdens among families with and without mental health problems. On average, families incurred 44% of non-mental health and 37% of out-of-pocket mental health treatment expenditures in a single month. Families with one or more members experiencing mental health problems were more likely to have periods of high out-of-pocket spending burdens. However, this study found that mental health treatment itself contributes little to high out-of-pocket spending burdens. Most of the burden was due to other medical conditions and lower average incomes among families with mental health problems.