Problem-based learning as an educational practice continues to have large impacts on all levels of education and across different disciplines. The aim of this study is to investigate the research trends in studies of problem-based learning (PBL) from 2002 to 2013 in Turkey. For this purpose, the master's and doctoral dissertations in the National Thesis Database of Council of Higher Education (CoHE) were selected for rigorous content analysis. The analysis was utilized to classify the type of study, the learning domains, research designs, research domains, subject groups, group sizes, and length of treatments. For analysis purposes, frequencies and percentages were calculated for each category. According to analysis results, science is the most favorable learning domain, quantitative design is more utilized as compared to qualitative and quantitative design, cognition and affect followed by cognition only are the mostly utilized research domains, subject groups are predominantly at elementary education level and secondly from teacher education, studies preferred to have a group size of 41-80, and finally the experimental treatments on PBL research last mostly 4 weeks and 6 weeks. (C) 2015 The Authors. Published by Elsevier Ltd.