BACKGROUND AND AIMS: The prevalence of alcohol-related conditions is often reported as higher in hospital in-patients compared with the general population. However, formal prevalence estimates are commonly derived from small studies which report highly varied results. This systematic review and meta-analysis, within the UK hospital system, aimed to estimate the pooled prevalence of the 26 ICD-10 conditions that are wholly attributable to alcohol in in-patient settings. METHODS: We searched Medline, Embase, PsychINFO and CENTRAL from database inception until 1 May 2018. We included studies of any design that reported the prevalence of one of 26 wholly attributable alcohol conditions defined by the ICD-10. Studies were required to be conducted in one or more of the constituent nations of the United Kingdom and in an in-patient setting (general wards, intensive care units, accident and emergency departments or mental health in-patient units). Estimates were pooled using random-effects meta-analysis, and meta-regression tested study and patient factors contributing to variation. Quality was assessed using the Grading of Recommendations Assessment Development and Evaluation (GRADE) framework. RESULTS: A total of 124 studies were included, reporting on a total of 1 657 614 patients. The majority of studies reported on harmful use of alcohol and alcohol dependence, for which the pooled prevalence was 19.76% [95% confidence interval (CI) = 15.61-24.26%] and 10.25% (95% CI = 7.06-13.96%), respectively. Mean patient age and type of in-patient setting were identified as the main sources of variation in prevalence estimates, but not date of data collection. Both estimates were deemed very low quality according to GRADE. CONCLUSIONS: An estimated one in five patients in the UK hospital system use alcohol harmfully, and one in 10 are alcohol-dependent.