The purpose of this study was to attempt to verify the existence of a relationship between internal resources (self-esteem and self-efficacy) and motivation (decisional balance) to undergo treatment in prisoners with alcohol addiction participating in voluntary treatment as well as referred to obligatory addiction treatment based on a court decision. The study was carried out in penitentiary units in various parts of Poland in 2018–2019. Participants completed the Decision Balance Scale, Generalized Self–Efficacy Scale, and Multidimensional Self-Esteem Inventory twice – before and after addiction treatment. The study adopted the assumptions of the Transtheoretical Model developed by Prochaska and DiClemente (1984). There were no statistically significant differences between the group of prisoners referred for obligatory treatment and those undergoing voluntary therapy. At the end of the 3-month treatment, there was a significantly smaller number of arguments “for” drinking and less identity integration in both groups studied. The results obtained may indicate that after undergoing therapy, prisoners remain in a contemplation stage due to their inability to adapt therapeutic interactions to individual needs. It seems that changes in identity integration may be indicative of the crisis that is being experienced, which in effect may allow individuals with alcohol addiction to search for and achieve a potentially new, coherent image of themselves.