To determine the prevalence of adherence to iron supplementation and the risk factors for incomplete adherence during the first year of life of infants in Izmir, Turkey. In this cross-sectional study, a total of 511 infants aged 2 to 12 months who presented to the Pediatrics outpatient clinics of Ege University Children's Hospital were included. Mothers (n = 511) who agreed to participate in the study were interviewed face-to-face and a comprehensive questionnaire including questions about the sociodemographic characteristics of the children and the family, and their adherence to iron supplementation was administered. The data obtained from 471 (92.2%) mothers who used iron supplements for their babies were subjected to further statistical analysis. Analyses were performed with SPSS 25.0. Chi-square test was used for univariate analysis and logistic regression analysis was used to determine the independent factors associated with incomplete adherence to iron supplementation. A total of 511 mothers were surveyed. Among the infants of mothers who participated in the study, 471 (92.2%) were taking iron supplementation. Of the infants who received iron supplementation, 58.3% were given iron supplementation with complete adherence. The percentage of complete adherence with iron supplementation was 35.1% between 2 and 4 months, 66.3% between 5 and 8 months, and 52.4% between 9 to 12 months. In univariate analysis, statistically significant differences were found between complete and incomplete adherence to iron supplementation in terms of infant age, time of birth, family income, maternal education, and maternal employment status (P < .001). When the data were analyzed using multivariate analysis, only maternal education level and infant age group were found to be statistically significant independent variables for complete and incomplete adherence to iron supplementation (P < .001). In populations with a high prevalence of ID, incomplete adherence to iron supplementation is a serious risk factor for ID/IDA. Although iron supplements are routinely given to infants by the Ministry of Health in Turkey, the prevalence of complete adherence to iron supplementation is low. Therefore, in order to increase the rate of complete adherence to iron supplementation, the iron supplementation status of infants should be reviewed in detail at each health child visit and families should be informed about the importance of supplementation to prevent iron deficiency.