<b><i>Objective:</i></b> Substance use among incarcerated people is prevalent in prisons worldwide. Little is known, however, about the factors associated with substance use during incarceration. Of special interest is the role of childhood abuse and social support on prison-based substance use, as these variables have been found to influence the use of alcohol and drugs in the community.

<b><i>Method:</i></b> We used a random sample of 943 male inmates in southeast Spain to estimate the prevalence and pattern of substance use during the past 3 months of incarceration. Using logit modeling techniques, we assessed the relationship between substance use in prison and measures of childhood abuse, social support, and resiliency.

<b><i>Results:</i></b> Childhood trauma experiences were most prevalent among mono- and poly-substance-use groups and were strongly associated with prison-based substance use. Social support and resiliency were highest among substance nonusers and served a protective role: Higher levels of external or internal support reduced the likelihood of prison-based substance use.

<b><i>Conclusions:</i></b> Findings point to the need for additional training for social workers and correctional personnel in understanding patterns of prison-based substance use.