The validity and credibility of scientific research are determined by the strictness of planning and elaborating each stage of the research, by correlating the purpose of the research with the chosen research method, by avoiding methodological planning errors, as well as by carrying out each research stage in a manner that excludes errors in data collection, processing and interpretation. In the field of social work, par excellence, the value of an empirical research is conferred, among other things, by the possibility of extrapolating the conclusions of that research to similar situations in the practical activity of social workers, in case work with the beneficiaries of social work services. Due to the close connection between research and practice in this field of social sciences, the methodological design must be transparent and convincing, so as to give practitioners a high degree of confidence in the conclusions of the scientific study, as well as the possibility to capitalize on its informative benefits. So, methodological errors of research projects carried out in the field of social work can have a much wider and more tangible negative impact than in the case of other fields of science, at least from a pragmatic point of view, when theory is translated to practical applicability, and the scientific study is implemented in case work performed with the beneficiaries. This study aims to analyze the questionnaire survey in social work, by highlighting the main methodological errors that can affect the validity of such an empirical study, in order to identify the optimal solutions for a correct planning and methodological development of the scientific study.