Background: In the United Kingdom, policy change has led to specialist intellectual disability inpatient bed reduction. Little evidence exists assessing the results for patients admitted to such units. This study evaluates the outcomes of a specialist intellectual disability inpatient unit. Method: Gender/age/ethnicity/intellectual disability severity/co-morbid psychiatric/developmental disorders, treatment length and stay data were collected. The health of the nation outcome scales for people with learning disabilities (HoNOS-LD) scores at admission, treatment completion and discharge were recorded. Analysis of these multiple variables and correlations within different patient groups was investigated using various statistical tests. Results: Of 169/176 patients (2010-2018), admission to discharge, HoNOS-LD global and all individual items score decreased significantly, for all patient categories. Treatment completion to discharge duration was significant for the whole cohort. Conclusions: This is the largest study of intellectual disability inpatient outcomes. Discharge from the hospital appears not associated with duration of treatment. Using HoNOS-LD to demonstrate treatment effectiveness is recommended.