Background: To determine vitamin D supplementation frequency among infants, factors that influence adherence, and reasons for discontinuation of initiated vitamin D. Methods: This cross-sectional study was conducted using a questionnaire administered to the mothers via a face-to-face interview on 560 infants aged from 1 to 24 months admitted to outpatient clinics from June to December 2017. Results: A total of 351 infants were administered vitamin D, and the rate of supplementation in the first year of life was 83%, while it was only 28% between 13 and 24 months. The rate of vitamin D supplementation was higher among infants who were exclusively formula-fed (p<.05). When the data were analyzed using logistic regression analysis, only visit family physicians seems to be a statistically significant independent variable in increasing supplementation (p<.05). Compared with family refusal, the rate of discontinuation of vitamin D by the healthcare providers was higher after the first year of life (p<.05). The rates of vitamin D discontinuation by healthcare providers, especially by nurses who considered the duration of supplementation adequate, were statistically significantly higher when compared with the fontanel closure and other reasons (p<0.05). Conclusions: The rate of vitamin D supplementation was higher among families who visited family physicians, which suggests the importance of well-baby visits. Since vitamin D supplementation was less common among exclusively breastfed infants, mothers should be educated. Healthcare professionals need further education about the importance of vitamin D supplementation and indications for discontinuation.