A standard definition of outpatient mental health care does not now exist. Data from the 1987 National Medical Expenditure Survey are used to examine how varying the definition influences utilization estimates. A broad definition of mental health care, which requires purchase of a psychotropic medication or a psychotherapy visit or a visit for a mental health condition, captures nearly seven times as many persons as a definition that requires a visit to a mental health specialist for a mental health condition and either purchase of a psychotropic medication or psychotherapy. Because estimates of mental health service use are highly sensitive to how treatment is defined, caution should be exercised in evaluating mental health utilization data.