We report on a new measure of maternal affect from an ongoing multi-site birth cohort study with primarily low-income families, the Fragile Families and Child Wellbeing Study. At child age of 5?years, mothers were asked to describe their child in a short, semi-structured home interview. One innovation of this measure--called the Maternal Description of Child (MDoC)--is that it captured maternal affect via audiotape rather than videotape. Based on mothers' talk about their child, coders scored mothers on Positive Affect, Negative Affect, and Detachment. Evidence is presented to support the convergent and predictive validity of these scales. Given that objective measures of parenting are generally preferable to self-reported measures, further research should determine whether the MDoC can be successfully administered by phone. If it can, the MDoC would allow large-scale phone surveys to measure maternal affect for the first time.