An accurate assessment of stroke severity and the ability to predict prognosis is important for determining rehabilitation needs and long term management of patients after stroke. The Orpington Prognostic Score (OPS) is a clinically derived stroke severity scale that can be used to stratify patients into different severity groups. The aim of this study was to validate the Orpington Prognostic Score (OPS) in an Irish in-patient stroke population. Fifty 'first stroke' patients (21 male, median age 72.5 [range 31-93] years) were assessed within two weeks following stroke onset. Subjects were stratified into mild, moderate and severe groups using previously established cut-offs for the OPS. Outcomes were determined prospectively and compared to initial severity groups. Patients in the severe group had a significantly increased chance of dying (Odds ratio [95%CI] 2.16 [1.72-2.72] and this persisted after adjustment for age and gender. Length of stay increased significantly with increasing stroke severity group (F ratio 7.0 p=0.0025) and this association remained after adjusting for age and gender. The odds of being discharged home or of being able to walk independently by time of discharge decreased significantly (all p<0.001) as stroke severity increased and adjusting for age and gender did not alter these associations. A higher OPS score within 2 weeks of stroke onset was significantly associated with longer length of stay, increased mortality, reduced mobility at discharge and a reduced likelihood of discharge home. The OPS is a valid measure of stroke severity in Irish stroke in-patients.