Background Although most biomedical journals have adopted the authorship criteria established by the International Committee of Medical Journal Editors (ICMJE) in 1985, little is known about the extent Iranian researchers are familiar with these criteria. Objectives The study seeks to evaluate the number of authors fulfilling ICMJE authorship criteria (considering the names mentioned in the byline of 12 issues of the Archives of Iranian Medicine (AIM) journal), and to determine the type of contribution made by each author. Materials and Methods The fulfilment of authorship criteria and contribution percentage of each researcher were evaluated according to their position in the bylines of 12 issues of the Archives of Iranian Medicine (AIM) journal published from January 2005 to October 2007. We asked corresponding authors to answer our questionnaire which was designed to assess authorship criteria and contribution. Results A total of 576 researchers' names were in the studied article bylines. The ratio of authors to articles was 3.48 in 2005, 4.06 in 2006, and 5.59 in 2007. Sixty three out of 128 corresponding authors (49.21%) responded to our questionnaire, so we evaluated 296 researchers' names, from which 186 authors (62.83%) met the authorship criteria; 110 authors (37.17%) were identified as guest authors, 97 of which deserved to be mentioned in the acknowledgement section. The major criteria used for authors order was their participation in research projects in addition to article writing, mostly determined by the corresponding author. Two authors (0.67%) whose names were not mentioned in the articles were considered to be ghost writers as the articles were based on the results of their thesis. Conclusion It is essential to make Iranian researchers familiar with ICMJE authorship criteria and to encourage applying the criteria in scientific writing.