The aim of this paper is to examine the prevalence of substance use among fi rst-year stu-dents at the University of Mostar, Bosnia and Herzegovina, and to determine differences with regard to the socio-demographic characteristics of the participants. The study was conducted in June 2012 by teaching assistants at the Department of Social Work, Faculty of Humanities and Social Sciences, University of Mostar, in collaboration with social work students who were previously trained to conduct the research. The study included 420 participants from six faculties. The research is designed to determine which substances are most frequently used among fi rst-year students and to determine whether there are differences in the frequency of alcohol consumption, smoking and drug use among students with regard to their socio-de-mographic characteristics. The results show that the most frequently used substance among students is alcohol; cigarettes are in second place and marijuana (as the only drug with si-gnifi cant frequency of consumption) in third. Some socio-demographic characteristics have proven to be signifi cant in the frequency of substance use.