Long-term weight-loss maintenance is notoriously difficult to achieve and promote. As the novelty of weight loss treatment fades, enthusiasm for diet and exercise tends to wane in the maintenance phase. Given the recognition of obesity as a chronic disorder requiring continued engagement in weight-control behaviors, there is a need to identify cost-effective and supportive therapies that can sustain motivation. In this paper, we describe the study design and baseline characteristics of participants enrolled in a trial to evaluate a program (Keep It Off) developed specifically for weight-loss maintenance using therapeutic phone contact with recent weight losers throughout the period in which they are at highest risk for weight regain. In the Keep It Off randomized clinical trial we are evaluating this phone-based intervention that focuses on key weight-loss maintenance behaviors followed by continued self-monitoring, reporting of weight, feedback, and outreach in members of a Minnesota managed-care organization. The goal of the intervention is to flatten the typical relapse curve. Moreover, data from this trial will inform our understanding of weight-loss maintenance, including predictors and behaviors that increase the likelihood of success over the long term.