Chronic non-cancer pain (CNCP) is significant global health issue, accounting for a substantial increase in prescription analgesics worldwide, in recent decades. This clinical burden is evident in the UK prison population, where the prevalence of CNCP has never previously been determined. This study, conducted in June/July 2013, used prescribing data and a systematic review of clinical records from two UK prison establishments to derive a figure for point-prevalence of CNCP. Results showed that 20% of the total aggregated prisoner rolls (N = 1944) described CNCP and had been in receipt of treatment with daily analgesia, for a period of at least 3 months prior to observation date. This prevalence of CNCP was related to increasing age group (Spearman’s rank correlation 0.94). Of those on continuous analgesic therapy (CAT), 44% were taking continuous opioid therapy (COT) of any sort. Prisoners with a diagnosis of opioid-type drug dependence (OTDD) were more than twice as likely to complain of CNCP and be on continuous medication for it (odds ratio 2.3). The issues relating to CNCP in prisons are discussed. Further research is recommended, identifying factors influencing CNCP prevalence in prisons, and enabling comparisons to CNCP prevalence in the UK general population.