The Subacute Care Units (SCU) have been created to provide integrated care to fragile and/or comorbid elderly people with exacerbated chronic diseases or minor acute events. This units are provided with low technology but with geriatric expertise. Direct admission from emergency departments (ED) has been promoted, to reduce unnecessary acute hospital admissions and overcrowding in ED. One of the serious complications in the clinical evolution of subacute patients is delirium, not only due to high incidence, but also due to the strong negative impact. Methods Prospective cohort study of consecutive patients admitted to the SCU of Parc Sanitari Pere Virgili (Barcelona) between 2012 and 2016. A comprehensive geriatric assessment (CGA) was performed in all patients and their clinical and functional results were collected at discharge and 30 days post-discharge, including 30 days readmission. First part of the work focuses on the profile and clinical results of patients admitted to the SCU; the second part analyzes the impact of delirium (prevalence, motor subtypes, mortality, functional loss and clinical results) on these patients. Additionally, a sub-study based on an international multicenter cohort carried out outside the SCU, which aims to improve the diagnosis of delirium in patients with dementia, is incorporated. Results Between 2012 and 2016, 1477 patients were admitted to the SCU (mean age 85.6 years, 62,6% women). 89.6% were directly transferred from the ED. The CGA showed a moderate functional dependence (previous Barthel Index=57.8), high comorbidity (Charlson=2.7), high prevalence of diabetes mellitus (33.1%), dementia (41.6%) and polypharmacy (8.5 drugs per patient). After an average hospital stay of 10 days, 75% of patients returned to their usual living situation, 13.1% required admission to long-term nursing care, 3.9% were admitted to the acute hospital and 6.9% died. 30-days readmission rate was 16.4%. Despite the greater complexity of patients identified as Complex Chronic Patient or with Advanced Chronic Disease (PCC/MACA), the clinical results at discharge were similar to patients with lower complexity. However, at 30 days post-discharge, these patients presented higher mortality (15,4% vs. 8%; p=0,010) and more readmissions (18.7% vs. 10.5%; p=0.014). In order to optimize the selection of patients admitted to the SCU, high scores on the ISAR scale predicted worse results at discharge (AUC = 0.65). Prevalence of delirium was 38.7%, increasing to 65.1% among patients with dementia. Development of delirium led to higher mortality and lower return to the usual living situation, along with worse functional results, a consequence also observed in patients developing delirium superimposed on dementia (DSD). Hyperactive delirium was most frequent (40.6%), followed by mixed (31%) and hypoactive (25.9%). The hypoactive subtype, more frequent in high vulnerable patients, was associated with worse clinical and functional results. In the multicenter sub-study performed outside the SCU, the assessment of motor aspects through the Hierarchical Assessment of Balance and Mobility (HABAM) could improve the diagnosis of DSD. Conclusions Patients admitted to the SCU represent a very old population, with important comorbidity, high prevalence of dementia and moderate functional dependence. Despite the high complexity in the management and care of these people, more than 75% return to their usual living situation at discharge. On the other hand, the high prevalence of delirium in these patients (39%) has allowed to determine a severe impact of the delirium not only in clinical results (increase in mortality, lower return home), but also its negative impact on the functional trajectory. As a global conclusion, our results show that the SCU might be a useful resource in addressing these patients and provide adequate health care, which could most likely improve with the implementation of strategic and proactive delirium prevention plans.