This study investigated parenting stress trajectories among low-income young mothers and the factors that are associated with change and stability of parenting stress as children aged from 14 to 36 months old. With a sample of 580 young mothers who applied to the Early Head Start Program, growth mixture modeling identified 3 trajectory classes of parenting stress: a chronically high group (7% of the sample), an increasing group (10% of the sample), and a decreasing group (83% of the sample). Maternal personal resources distinguished between the increasing and decreasing classes, whereas maternal personal resources, child characteristics, and contextual influences explained differences between the chronically high and decreasing trajectory classes. Findings suggest that for interventions to be effective, programs need to assess maternal, child, and contextual factors to better address the particular unique needs of young mothers. (author abstract)