Objectives The burden of multimorbidity is increasing worldwide; however, little is known about trends in multimorbidity prevalence among Chinese older adults. We aimed to estimate the prevalence and trends of multimorbidity in community-dwelling older adults in Beijing. Design Longitudinal. Setting and participants Residents of Beijing aged >= 60 years. Measurements Data were derived from the Beijing Longitudinal Study of Aging, using cluster, stratification, and random sampling. A total of 1842, 2914, and 1837 participants were included in the 2004, 2011, and 2017 sample, respectively. Multimorbidity was defined as the presence of two or more chronic conditions. Trends in multimorbidity were examined by age, sex, and geographical area. Results The prevalence of multimorbidity was 32.5%, 52.9%, and 53.2% in 2004, 2011, and 2017, respectively, following an upward trend over time (P =0.003). A similar multimorbidity increase trend was present in age-, sex-, and region-stratified analysis for the 2004-2017 period (all P<0.05). The most common chronic diseases in 2004 were hypertension (34.3%), cataract (18.2%), coronary heart disease (CHD) (15.6%), stroke (14.3%), and chronic obstructive pulmonary disease (7.9%); in 2011, these were hypertension (49.6%), arthritis (30.9%), CHD (22.3%), stroke (21.9%), and diabetes (15.1%); in 2017, these were hypertension (54.4%), arthritis (26.3%), stroke (22.6%), cataract (20.5%), and CHD (20.1%). The proportion of older adults diagnosed with >= 3 chronic diseases significantly increased from 13.4% in 2004 to 73.1% in 2011 and 69.5% in 2017. Conclusions Multimorbidity is common and the overall and age-, sex-, and region-specific multimorbidity prevalence has been increasing over the past 13 years. Public health policies should account for the more complex care needs and growing costs associated with increasing prevalence of chronic disease and multimorbidity in Chinese older adults.