BACKGROUND B cell-activating factor (BAFF) is a tumour necrosis factor superfamily member best known for its role in the survival and maturation of B cells. BAFF activity is seen in naïve and effector/memory T cells. OBJECTIVE To investigate the level and role of BAFF in serum of patients with atopic dermatitis (AD). METHODS Levels of serum BAFF, a proliferation-inducing ligand (APRIL) and total serum IgE level, and total eosinophil count were measured in 245 children. RESULTS Patients were characterized as having atopic eczema (AE) (n = 90) or non-AE (n = 77); the remainder were healthy control subjects (n = 78). Serum BAFF level in children with AE (1625.04 +/- 708.32 pg/mL) was significantly higher than in non-AE children (1194.69 +/- 448.44 pg/mL, P < 0.0001) or healthy controls (1062.89 +/- 444.74 pg/mL, P < 0.0001). Serum APRIL level was not different between the three groups. Serum BAFF level significantly correlated with total serum IgE level (gamma = 0.42, P < 0.0001) and total eosinophil count. It was also positively correlated with serum BAFF and egg-specific IgE level (gamma = 0.252, P = 0.045) in AE. CONCLUSIONS Serum BAFF level is high in AE and might be a useful marker for AE.