ObjectiveTwo-thirds of the economic resources in Norwegian hospitals are used on 10% of the patients. Most of these high-cost patients are older adults, which experience more unplanned hospital admissions, longer hospital stays and higher readmission rates than other patients. This study aims to examine the individual and clinical characteristics of older patients with unplanned admissions to Norwegian somatic hospitals and how these characteristics differ between high-cost and low-cost older patients.DesignObservational cross-sectional study.SettingNorwegian somatic hospitals.ParticipantsNational registry data of older Norwegian patients (≥65 years) with ≥1 unplanned contact with somatic hospitals in 2019 (n=2 11 738).Primary outcome measureHigh-cost older patients were defined as those within the 10% of the highest diagnosis-related group weights in 2019 (n=21 179). We compared high-cost to low-cost older patients using bivariate analyses and logistic regression analysis.ResultsMen were more likely to be high-cost older patients than women (OR=1.25, 95% CI 1.21 to 1.29) and the oldest (90+ years) compared with the youngest older adults (65–69 years) were less likely to cause high costs (OR=0.47, 95% CI 0.43 to 0.51). Those with the highest level of education were less likely to cause high costs than those with primary school degrees (OR=0.74, 95% CI 0.69 to 0.80). Main diagnosis group (OR=3.50, 95% CI 3.37 to 3.63) and dying (OR=4.13, 95% CI 3.96 to 4.30) were the clinical characteristics most strongly associated with the likelihood of being a high-cost older patient.ConclusionSeveral of the observed patient characteristics in this study may warrant further investigation as they might contribute to high healthcare costs. For example, MDGs, reflecting comprehensive healthcare needs and lower education, which is associated with poorer health status, increase the likelihood of being high-cost older patients. Our results indicate that Norwegian hospitals function according to the intentions of those having the highest needs receiving most services.