No prior studies have examined how interventionists’ perceptions of participants’ weight control challenges or the agreement between participants and interventionists on these perceptions relate to outcomes during group-based behavioral weight loss treatment. This study characterized participants’ and interventionists’ perceptions of, and agreement about, weight control challenges and assessed how these factors relate to weight loss. Three months into treatment, participants and interventionists independently selected three weight control challenges believed to be most relevant for each participant. Weight was measured at baseline, 3 months, and 12 months. Interventionists and participants had “no” (κ < 0) or “slight” (0 < κ< .20) agreement on most challenges. Although endorsement of certain challenges by participants and/or interventionists was related to 3- and 12-month weight losses, agreement between participants and interventionists was unrelated to weight loss at either time point. Additional research is needed to better understand the role of perceived challenges and participant/interventionist agreement about challenges on treatment outcomes.