IntroductionThe development of multiple coexisting chronic diseases (multimorbidity) is increasing globally, along with the percentage of older adults affected by it. Multimorbidity is associated with the concomitant use of multiple medications, a greater possibility of adverse effects, and increased risk of hospitalisation. Therefore, this systematic review study protocol aims to analyse the impact of multimorbidity on the occurrence of hospitalisation in older adults and assess whether this impact changes according to factors such as sex, age, institutionalisation and socioeconomic status. This study will also review the average length of hospital stay and the occurrence of hospital readmission.Methods and analysisA systematic review of the literature will be carried out using the PubMed, Embase and Scopus databases. The inclusion criteria will incorporate cross-sectional, cohort and case–control studies that analysed the association between multimorbidity (defined as the presence of ≥2 and/or ≥3 chronic conditions and complex multimorbidity) and hospitalisation (yes/no, days of hospitalisation and number of readmissions) in older adults (aged ≥60 years or >65 years). Effect measures will be quantified, including ORs, prevalence ratios, HRs and relative risk, along with their associated 95% CI. The overall aim of this study is to widen knowledge and to raise reflections about the association between multimorbidity and hospitalisation in older adults. Ultimately, its findings may contribute to improvements in public health policies resulting in cost reductions across healthcare systems.Ethics and disseminationEthical approval is not required. The results will be disseminated via submission for publication to a peer-reviewed journal when complete.PROSPERO registration numberCRD42021229328.