There is an absence of research on gambling among prison inmates during their incarceration. Little is known about how prisoners organize gambling activities or the potential risks they face from gambling. Similarly, no empirical attention has been given to how correctional institutions respond to inmate gambling. This study employed interviews with 55 male prisoners and self-administered surveys with 159 correctional officers and staff, at two medium security prisons in Ohio. Data were gathered on prevalence and patterns of inmate gambling, perceived hazards of gambling, and perceived institutional responses to prisoner gambling. Findings suggest that inmate gambling is common and constitutes an important feature of the underground economy of prisons, yet little is done to deter or prevent this activity. Suggestions are made for more effective institutional responses.