International studies find that between a quarter and a third of offenders may be defined as problem gamblers. No comparable studies have been conducted in the UK during the last decade, which has seen unprecedented changes in gambling legislation and opportunities. The present study in two English prisons (one male and one female) found that levels of problem gambling were in line with global estimates. 27.8% of men and 18.1% of women were rated as medium-risk and problem gamblers. Gambling problems were linked to current and previous offending for between 7% and 13% of all offenders.