Recently, we conducted a nationwide survey on FPD in broilers and reported its high and wide prevalence in Japan, although the incidence varies among farms [13]. In Europe, litter moisture has been linked to the development of FPD in broiler chickens and turkeys [14,15,16,17, 20, 22]. It appears that the wetter the litter is, the more likely that FPD will develop. Although Japan is a country of high humidity throughout the year, the association between litter moisture and FPD has not been studied. The purpose of the present study, therefore, was to investigate the effect of litter moisture on the development of FPD among Japanese broiler chickens.