Background Hemoglobin A1c (HbA1c) is the major form of glycosylated hemoglobin. There are conflicting data on changes in HbA1c levels in patients with iron deficiency anemia (IDA). The present study aimed to investigate the effects of HbA1c levels in the presence of IDA, the effects of iron treatment on HbA1c levels, as well as the relationship between the severity of anemia and HbA1c levels in patients without diabetes. Design and methods A total of 263 patients without diabetes mellitus (DM) who were admitted to Cukurova University, Faculty of Medicine, Department of Endocrinology and Hematology or who were followed up in this clinic and diagnosed as having IDA were included in the study. A total of 131 patients had IDA. The control group comprised 132 age-matched and sex-matched healthy individuals. Results The mean HbA1c level was significantly lower in the group with IDA (5.4%) than in the healthy control group (5.9%; p & x202f;< 0.05). When the patients were divided into three groups according to the severity of anemia through Hb levels, HbA1c levels were observed to decrease as the severity of the anemia increased (5.5%, 5.4%, and 5%, respectively; p & x202f;> 0.05). The HbA1c levels of the patients with IDA were higher after iron therapy (from 5.4 & x202f;+/- 0.5 to 5.5 & x202f;+/- 0.3; p & x202f;= 0.057). The mean hemoglobin (Hb), hematocrit (Hct), mean cell volume (MCV), mean corpusculer hemoglobin (MCH), and ferritin values also increased after iron therapy (p & x202f;< 0.05). Conclusion The study results showed that IDA was associated with low HbA1c levels, and increased after iron therapy. Based on the study findings, it is necessary to consider the possible effects of IDA on HbA1c levels.