BACKGROUND: Multimorbidity predicts a worse prognosis for various diseases but its impact in people after an acute ischemic stroke (AIS) in developing societies is not well established. We aimed to characterize the pattern of multimorbidity and determine its association with in-hospital mortality after AIS in the nationwide Chilean database. METHODS: A retrospective analysis of the Diagnosis-Related Groups database for hospitalized adult patients in Chile in 2019 was conducted. Association of multimorbidity, defined as the presence of ≥2 health conditions, in patients with AIS (ICD-10 code I63) on in-hospital mortality was determined in logistic regression models adjusted for confounding variables. RESULTS: Of 1,048,575 recorded ICD-10 codes, there were 10,440 AIS episodes in whom 7,696 (73.7 %) patients had multimorbidity. Age, female sex, and low socioeconomic status were associated with a higher multimorbidity, and the combination of comorbidities differed across age groups. Cardiometabolic multimorbidity was associated with higher in-hospital mortality (odds ratio [OR] 1.39, 95 % confidence interval [CI] 1.16-1.66
p<
0.002). Stage 5 chronic kidney disease combined with ischemic heart disease was the comorbidity with the highest risk of death (OR 4.20, 95 %CI 1.58-11.16
p = 0.004). Obesity, which exhibited a predominance in early to mid-life, had the highest association with mortality when combined with other conditions. CONCLUSIONS: Multimorbidity is common in patients with AIS and its components vary by age and sex. Cardiometabolic multimorbidity increases the likelihood of in-hospital mortality. Adopting a multimorbidity-focused approach to stroke care could improve outcomes.