The relationship between iron body status and different types of hair loss has been investigated in a number of studies, however, with relatively discrepant findings. Therefore we conducted an analytical case-control study to assess whether diffuse telogen hair loss in women of childbearing age (15 to 45 years old) is associated with iron deficiency. Using the analytical case-control methodology, we studied 30 consecutive women with documented diffuse telogen hair loss in comparison with 30 women without hair loss. Study subjects had no history of nutritional supplement intake or chronic underlying diseases, and had normal thyroid function and inflammatory profiles. Biochemical investigations were performed in all study women. The mean ferritin level and trasferrin saturation was statistically significantly lower in patients with diffuse telogen hair loss than in subjects without hair loss (16.3+/-12.6 vs. 60.3+/-50.1, ng/mL; P<0.0001 and 20.3+/-9.7 vs. 28.3+/-11.8 percent; P=0.006, respectively). Also, total iron binding capacity was significantly higher in patients than in control group (367.8+/-58.2 vs. 319.2+/-60.1 microg/dL; P=0.004). Of nine patients with iron deficiency anemia (Hb <12 g/dL), eight patients had telogen hair loss (odds ratio: 10.5, 95%CI: 1.2-90.7; P=0.013). Odds ratio (95% confidence interval) for diffuse telogen hair loss was 21.0 (4.2-105.0) at serum ferritin levels < or =30 ng/mL. Women with iron deficiency status are at a risk of telogen hair loss. The important role of serum ferritin in hair loss is becoming more evident. In women without systemic inflammation or other underlying disorders, serum ferritin levels below or equal to 30 ng/mL are strongly associated with telogen hair loss.