Treatment motivation is required for virtually all psychosocial treatments because clients must participate actively in the treatment process. In child and family treatments, it is the parent who must be motivated to manage treatment participation; however, no measures are currently available for evaluating parent motivation for treatment. The authors developed and evaluated a brief rating scale, the Parent Motivation Inventory (PMI), to measure parent motivation to participate in treatment. Results supported a uni-dimensional measure with strong internal consistency and test-retest reliability. Increases in parent motivation predicted the perception of fewer barriers to treatment participation, which was significantly associated with greater treatment attendance. The PMI provides a reliable and valid method of assessing parents' motivation to participate in treatment and has implications for the prediction and potential modification of barriers to treatment and treatment participation.