Background & Aims: One of the important goals of research studies especially in medical sciences is accurate measurement of outcome occurrence. Despite numerous efforts to reduce accuracy errors, they still occur. The aim of this study was to assess types of errors and their control methods in medical sciences studies.Materials & Methods: A comprehensive review of literature in the Internet was performed to cover most of the materials. key word of the review included bias, error, validity, and confounding. The medical databases were national and international such as IranMedex, IranDoc, PubMed, ScienceDirect, ProQuest and Ovid.Results: The literature review indicated that errors in medical sciences studies are caused due to accidental errors, biases, or sampling errors. In order to reduce study errors, attention to accuracy and validity of studies is necessary.Conclusions: It is recommended that researchers can identify and reduce potential sources of biases selecting a stronger study design, random allocation, matching, observer and interviewer blinding, validating instruments, and using multivariate statistical analysis.