This review examines the results of randomized controlled trials in which behavioral weight loss interventions, used alone or with pharmacotherapy, were provided in primary care settings. Literature search of MEDLINE, PubMed, Cochrane Systematic Reviews, CINAHL, and EMBASE (1950-present). Inclusion criteria for studies were: (1) randomized trial, (2) obesity intervention in US adults, and (3) conducted in primary care or explicitly intended to model a primary care setting. Both authors reviewed each study to extract treatment modality, provider, setting, weight change, and attrition. The CONSORT criteria were used to assess study quality. Due to the small number and heterogeneity of studies, results were summarized but not pooled quantitatively. Ten trials met the inclusion criteria. Studies were classified as: (1) PCP counseling alone, (2) PCP counseling + pharmacotherapy, and (3) "collaborative" obesity care (treatment delivered by a non-physician provider). Weight losses in the active treatment arms of these categories of studies ranged from 0.1 to 2.3 kg, 1.7 to 7.5 kg, and 0.4 to 7.7 kg, respectively. Most studies provided low- or moderate-intensity counseling, as defined by the US Preventive Services Task Force. Current evidence does not support the use of low- to moderate-intensity physician counseling for obesity, by itself, to achieve clinically meaningful weight loss. PCP counseling plus pharmacotherapy, or intensive counseling (from a dietitian or nurse) plus meal replacements may help patients achieve this goal. Further research is needed on different models of managing obesity in primary care practice.