This is the first study to address the association between litter moisture and the development of FPD in commercial farms in Japan, rather than in a laboratory environment. FPD has been described as contact dermatitis, because it develops in contact with litter that is high in moisture content [11]. It has been demonstrated that daily 8-hr contact with wet litter can cause FPD lesions on the skin of the foot in growing turkeys [22]. In the present study, broilers reared on wet litter developed FPD from an early age, and it progressed severely. When these broilers were moved to dry litter, however, the disease progression was suppressed or delayed depending on the age of transfer. These results suggest that FPD can be treated or at least improved by changing the litter conditions, even after the visible onset of disease.