The 1930s mark the beginning of changes in the Polish prison system. Both new prison regulations (1931) and a new penal code (1932) started a sweeping reform in the penal system of the Second Republic of Poland. The reform included the introduction of a committee subordinate to the department of justice, responsible for criminal and biological research. The most important task of the committee was to conduct research on a national scale. Studies were based on a questionnaire, specifically created for the task. each sentenced individual at the time was subject to the questionnaire. The starting point of this research was acknowledgment of the importance of individualization of sentenced individuals. The goal of the study was both to create a mass portrait of the criminal community, as well as individual evaluation of every prisoner. On the basis of such evaluation the most appropriate penal institution was chosen, such as a maximum security prison, psychiatric prison, or prison farm. The study conducted in the 1930’s covered 40 thousand prisoners and was interdisciplinary in nature. The questionnaire was composed of over a dozen parts and was meant to evaluate prisoners’ physical and mental condition. It included information such as medical history, current illnesses, detailed anthropometric description, criminal history, environment in which they lived and grew up in, attitude towards the committed crime and their conduct in prison. The questionnaire was created by representatives of several scientific disciplines, most significantly psychiatry and anthropology, but also criminology, prison studies and sociology. Prison officers, as well as doctors were directly involved in conducting the research. However, the questionnaire was not considered an ideal tool. Initiatives of the department of justice became an object of harsh criticism. The research method, as well as the questionnaire itself were under fire especially by criminologists at the time. During the 1944 uprising, the entire legacy of the commission was destroyed. Fortunately, several thousand questionnaires and prisoner records survived the interwar period. However, they are currently extremely dispersed. collecting, studying and analyzing them could become a starting point of research on the condition of interwar-period science, including evaluation of the work of its theoreticians and practitioners. The author of the article considers the questionnaires as an incredibly interesting source in research of the interwar period underclass, an environment which until recently has been considered unhistorical.