Prostaglandin D2 (PGD2 ) plays an important role in atopic dermatitis (AD) and 11, 15-dioxo-9α-hydroxy-, 2, 3, 4, 5-tetranorprostan-1, 20-dioicacid (PGDM) is a major metabolite of PGD2 . We investigated the relationship between the urinary-PGDM levels and the severity of pediatric AD. Thirty-one AD and 21 non-AD subjects were recruited, and urinary-PGDM levels were measured. 14 AD patients were assessed for urinary-PGDM after topical steroid therapy. There was no difference in urinary-PGDM levels between the AD patients and healthy subjects. Although there was a significant positive correlation between the SCORing of AD (SCORAD) index and the serum level of thymus and activation-regulated chemokine (TARC), the urinary-PGDM levels were not correlated with SCORAD and serum TARC. Moreover, SCORAD and serum TARC were significantly improved by topical steroid therapy; however, urinary-PGDM levels were not changed. The level of urinary PGD2 metabolites in AD children is substantially equal to that in heathy controls even if the disease is severe.