Research on morbidity and mortality often emphasizes individual diseases over the cumulative effects of multimorbidity, especially in low- and middle-income countries. This study aimed to analyze the association between multimorbidity and all-cause mortality in a representative sample of the Chilean population. This longitudinal study used data from 3701 subjects aged ≥15 years who participated in the Chilean National Health Survey conducted between 2009 and 2010. We included 16 self-reported highly prevalent morbidities. All-cause mortality data from an 11-year follow-up were collected from the Chilean Civil Registry. The Cox proportional hazard model, adjusted for confounders, determined the association between multimorbidity categories and all-cause mortality. Of the total sample, 24.3% reported no morbidity, while 50.4% two or more. After adjustment, participants with four or more morbidities had a 1.66 times higher mortality risk [95% confidence interval (CI): 1.03–2.67] than those without morbidities. The mortality risk increased by 10% for each additional morbidity [HR: 1.09 (CI: 1.04–1.16)]. Multimorbidity was common in the Chilean population and increased the mortality risk, which greatly challenges the health system to provide an integral and coordinated approach to healthcare.