Background & Aims: Availability of scientific research at high levels of evidence, provide an appropriate context for evidence-based nursing. This study aims to identify the levels of evidence of ...nursing theses and dissertations in type-one medical universities of Iran in a period of twenty years. Material ;Methods: This is a descriptive survey on 1810 nursing theses and 54 dissertations. The abstract and/or method section of the theses and dissertations during 1991-2010 was reviewed and then their levels of evidence were determined by comparing these data with the table of evidence-based research assessment. Descriptive analysis on data was performed using SPSS-PC (v. 16). Results: A large percentage of the theses (60.7%) and dissertations (92.6%) were at the 6th level of evidence. First and 5th levels of evidence were not seen in Masters Theses, and none of the 1st, 4th and 5th levels of evidence was found in PhD dissertations. The lowest percentages (1.9%) of theses were situated at the 4th level. Only 7.4% of the dissertations were at the 2nd & 3rd levels of evidence. The trend of theses and dissertations during this period revealed that the 6th level of evidence is dominant. However, during 2005- 2010 the trend changed into performing research at the 2nd & 3rd levels of evidence. Conclusion: The results revealed that the majority of theses and dissertations in all educational fields and faculties are at the lowest (6th) level of evidence during the studied period. Thus, regarding the importance of evidence-based practice for increasing the quality of nursing care, investigating approaches to promote and improve the level evidence of nursing theses and dissertations is recommended. Received: 18 Sep 2012 Accepted: 6 Dec 2012
