Abstract Background Frailty is a risk factor for presentation to the ED, in-hospital mortality, prolonged hospital stays and functional decline at discharge. Profiling the prevalence and level of frailty within the acute hospital setting is vital to ensure evidence-based practice and service development within the construct of frailty. The aim of this cross-sectional study was to establish the prevalence of frailty and co-morbidities among older adults in an acute hospital setting. Methods Data collection was undertaken by clinical research nurses and advanced nurse practitioners experienced in assessing older adults. All patients aged ≥ 65 years and admitted to a medical or surgical inpatient setting between 08:00 and 20:00 and who attended the ED over a 24-h period were screened using validated frailty and co-morbidity scales. Age and gender demographics, Clinical Frailty Scale (CFS), Charlson Co-morbidity Index (CCI) and admitting specialty (medical/surgical) were collected. Descriptive statistics were used to profile the cohort, and p values were calculated to ascertain the significance of results. Results Within a sample of 413 inpatients, 291 (70%) were ≥ 65 years and therefore were included in the study. 202 of these 291 older adults (70%) were ≥ 75 years. Frailty was investigated using validated clinical cut-offs on the CFS (not frail < 5; frail ≥ 5). Comorbidities were investigated using the Charlson Comorbidity Index (mild 1–2; moderate 3–4; severe ≥ 5). The median CFS was 6 indicating moderate frailty levels, and the median CCI score was 3 denoting moderate co-morbidity. In the inpatient cohort, 245 (84%) screened positive for frailty, while 223 (75%) had moderate-severe co-morbidity (CCI Mod 3–4, severe ≥ 5). No significant differences were observed across genders for CFS and CCI. In the ED, 81 patients who attended the ED were ≥ 65 years. The median CFS was 6 (moderate frailty), and the median CCI was 5 (severe co-morbidity level). Seventy-four percent (60) of participants screened positively for frailty (CFS ≥ 5), and 31% (25) had a CFS of 7 or greater (severely frail). Ninety-six percent (78) of patients had a moderate-severe level of comorbidity. No significant associations were found between the CFS and CCI and ED participants age, gender, and medical/surgical speciality usage. Conclusion There is a high prevalence of frailty and co-morbidity among older adults who present to the ED and require inpatient care. This may contribute to increased waiting times, lengths of stay, and the need for specialist intervention. With an increased focus on the integration of care for older adults across care transitions, there is a clear need for expansion of frailty-based services, staff training in frailty care and multidisciplinary team resources across the hospital and community setting.