Counterdependency, a concept that describes defensive activity against dependent strivings, especially wishes to be taken care of, is gradually receiving increased clinical recognition. Clinical observation suggests its importance in many women with postpartum depression (PPD). In this article we report the development of a new self-report instrument to assess counterdependency, the SB Counterdependency Inventory (SBCI). We test the instrument in a population of women visiting websites concerning PPD. We find the instrument to have high reliability, good convergent validity, and that it discriminates between a population with PPD and a control population. Our results with the SBCI help to empirically establish the role of counterdependency as a psychological feature that is associated with PPD.