Abstract Disclosure: K. Ezendu: Employee; Self; Eli Lilly & Company. G. Pohl: Employee; Self; Eli Lilly & Company. Stock Owner; Self; Eli Lilly & Company. C.J. Lee: Employee; Self; Eli Lilly & Company. Stock Owner; Self; Eli Lilly & Company. H. Wang: None. X. Li: Employee; Self; Eli Lilly & Company. Stock Owner; Self; Eli Lilly & Company. J.P. Dunn: Employee; Self; Eli Lilly & Company. Stock Owner; Self; Eli Lilly & Company. Background: Multimorbidity is an individual and healthcare system burden. Increased multimorbidity occurs with both excess weight and aging. We aim to determine the burden of multimorbidity as BMI class increases in various age groups of people with obesity or overweight. Methods: The study cohorts were derived from extracts of Optum’s de-identified Market Clarity Data with linked electronic health records (EHR) and claims database. Patients were classified into four weight classes based on their median body mass index (BMI) in 2019 [overweight (BMI 25 - <30kg/m2 or 23 - <25kg/m2 for Asians), class 1 obesity (30 - <35kg/m2 or 25 - <27.5 kg/m2 for Asians ), class 2 obesity (35 - <40kg/m2 or 27.5 - <40 kg/m2 for Asians), and class 3 obesity (≥40kg/m2)] and three age groups: 19-40, 41-65 and > 65 years. People were required to be continuously insured in 2018 and 2019 and have at least one BMI in 2019. People aged <19 or >80 years, with any BMI >60 kg/m2 or with deviation from their 2019 median BMI of ≥5%, cancer diagnosis, pregnancy or childbirth in 2018 or 2019, HIV/AIDS, Cushing disease or Prader-Willi syndrome were excluded. The presence, as of December 31, 2019, of 17 obesity-related comorbidities (ORCs) was determined using ICD-10 codes in EHR or insurance claims: heart failure, atrial fibrillation, cerebrovascular disease, coronary artery disease, peripheral artery disease, hypertension, dyslipidemia, asthma, depression/anxiety, osteoarthritis, gout, chronic kidney disease, obstructive sleep apnea, non-alcoholic steatohepatitis, low back pain, type 2 diabetes, reproductive diseases. Multimorbidity was defined as having 2 or more ORCs. Results: 2,147,223 people were analyzed. Mean age was 51 years with 25.1 %, 58.0%, and 16.9% in the 3 age groups 19-40, 41-65 and >65, respectively. Females were 52%; and Caucasians, 77.9%; Blacks, 11.8%; and Asians, 1.9%. For people aged 19-40 years, prevalence of multimorbidity was 12.3%, 17.8%, 23.5%, and 33.5% for overweight, class 1, class 2, and class 3 obesity, respectively; 41.5%, 51.3%, 58.6% and 66.6% for people aged 41-65 years; and 70.6%, 78.9%, 81.8% and 85.9% for people aged >65 years. Discussion and Conclusion: In people with obesity or overweight, the burden of multimorbidity increased as BMI classes increased regardless of age group. While multimorbidity was especially high in those >65years (70-85%), the younger age groups also had substantial burden of multimorbidity with one in three adults with class 3 obesity in age 19-40 group reporting multimorbidity. Further research is warranted on better understanding the adverse impact of weight-related multimorbidity on the individual and society. Presentation: Saturday, June 17, 2023