This systematic review examines the prevalence, determinants, and patterns of multimorbidity in primary care. The study included 39 eligible publications from 12 countries, covering a total of 70,057,611 patients. The prevalence of multimorbidity ranged from 12.9% to 95.1%, with age, lower socioeconomic status, and female gender being the most significant determinants. The most common patterns of multimorbidity included osteoarthritis combined with cardiovascular and/or metabolic conditions. The review highlights the need for standardized definitions and assessment methods to better understand and manage multimorbidity, as well as the importance of further research to inform policy and clinical practice.This systematic review examines the prevalence, determinants, and patterns of multimorbidity in primary care. The study included 39 eligible publications from 12 countries, covering a total of 70,057,611 patients. The prevalence of multimorbidity ranged from 12.9% to 95.1%, with age, lower socioeconomic status, and female gender being the most significant determinants. The most common patterns of multimorbidity included osteoarthritis combined with cardiovascular and/or metabolic conditions. The review highlights the need for standardized definitions and assessment methods to better understand and manage multimorbidity, as well as the importance of further research to inform policy and clinical practice.