Despite the increasing research in gambling, the prevalence of problem gambling in the criminal justice population is rarely investigated, especially in Europe. Given the lack in knowledge the Hamburg study aimed at identifying the prevalence of problem gambling in the whole regional prison population. For this purpose two major approaches were used: a 10 months long-term screening of pre-trial detainees at prison entry through the Lie/Bet Questionnaire, and full-scale survey of inmate personnel records of prisoners being in prison on a defined reporting date. Based on 792 valid screening files 6.6 % of the pre-trial detainees were positive on the Lie/Bet Questionnaire, and these problem gamblers were male only. Among the 1,236 inmate personnel records reviewed in 7.3 % the records indicated problem gambling (90 prisoners). This indication was found in 7.5 % males and 3.6 % females. For almost half of the prisoners with problem gambling their prison sentence was related to their gambling behavior (46.7 %). These results are representative for the regional prison population, and the first of its kind in Europe.