Our aims were to analyze the changes in hemoglobin (Hb) value according to gestational age, birth weight, sex, birth season, and weight gain and to detect distribution of Hb values among healthy infants, breastfed for at least four months and receiving routine health care. We conducted a descriptive study using the data of 469 healthy infants at 5-7 months of age in Hacettepe University Ihsan Dogramaci Children's Hospital Well-Baby Clinic between 2001-2004. Infants with acute or chronic illness, exchange transfusion and those who had taken or were currently taking iron supplementation were not included into the study. Information regarding the child was obtained from hospital files. Infants with Hb value <10.5 g/dl and <9.5 g/dl were considered to have mild and moderate anemia, respectively. The mean Hb value was 10.7 g/dl (SD = 0.90). The prevalence of anemia was 41.4%. Boys had significantly lower Hb, hematocrit and mean corpuscular volume values and higher red cell distribution width values than girls. Infants born before 37 weeks of gestational age had moderate anemia more frequently. Anemia at 5-7 months of age was more frequent in infants born in spring and summer than in those born in fall and winter (49.2%, 26.8%, p<0.001). Birth weight was positively correlated with Hb value at 5-7 months of age (r=0.14, p=0.003). In the present study, female gender, at-term birth, birth in winter and fall, weight appropriate for gestational age, and regular weight gain showed the lowest risk for anemia development in infants aged 5-7 months with a breast-feeding period of more than four months.