OBJECTIVE The objective of this study was to synthesise evidence from primary care-based interventions for the treatment of obesity in adults and the elderly. METHODS Systematic review. METHODS Eight electronic databases (MEDLINE, Lilacs, Embase, Psycinfo, Cochrane, WHOLIS, Open Gray and Scholar Google) were searched. There was no limitation on publication period; articles published in English, Portuguese or Spanish were included. The selection, data extraction and quality analyses were performed by three reviewers. RESULTS A literature search retrieved 6464 publications, of which 5120 publications were excluded after reading the title/abstract and 293 after reading the full text. In total, 56 publications, representing 72 interventions were included. All studies were published between 2000 and 2020. Most studies were conducted in high-income countries. The mean duration of interventions was 11.5 months (SD: 7.5), ranging from 3 to 44 months. Most interventions were effective for body mass index reduction, weight loss and waist circumference change. CONCLUSIONS Our study showed that most interventions were effective for outcomes analysed in adults and the elderly. We also found some literature gaps, such as the need to implement and evaluate obesity after intervention and the requirement to carry out more studies in low- and middle-income countries.