The inappropriate use of statistical method and technique cause time and cost losts and it can be misleading to other scientific researhes. So in this study the main statistical error sources in medical research are discussed and aimed to be informative for researchers. The most common statistical error sources are determined examining the previous medical researches and taking errors into account occured in researches during statistical consulting. Inappropriate use of statistics can be found in every stage of a medical research related to data analysis; design of the experiment, data collection and pre-processing, analysis method and implementation, and interpretation. We listed several error sources that researchers easily commit if they are lack of solid statistical background. The mistakes in the studies mostly occur because of the researchers’ lack of statistical knowledge and since they don’t take statistical consulting. Unbiased, consistent, and efficient parameter estimates are made in statistics science. This can be provided using statistics from the planning until the end of the study. So it is neccessary to consult statisticians at each stage of the studies.