The prevalence of Fatty liver syndrome (FLS) in laying flocks in Beni Suef, El Menia and Assiut Governorates was recorded through field observations of 23 laying flocks for one year. FLS was observed in 2 flocks of caged layers in El Menia and one flock in Assiut Governorates while no cases were observed in floor pen raised flocks. Cases of FLS were observed in summer months and the affected flocks showed drop in egg production (10-15%), increased monthly mortality (2.5%), enlarged, greesy, yellow livers with lipids, some cases had liver haemorrhages, more abdominal fat and more fat around the gizzard and proventriculus. Water hardeness was associated with appearance of FLS. The induction of FLS in laying hyline hens was experimentally studied using hard water, high atmospheric temperature, calcium deficient ration and aflatoxin. The results of experimental induction of FLS by these factors indicated that all of them can induce FLS as observed by clinical symptoms, pathological lesions, increase in body weight, liver weight, liver % of body weight, liver fat %, decrease in liver moisture and increase in certain serum constituents (GOT, cholesterol, triglycerides and total lipids).