Two cases of infantile liver cirrhosis of unknown origin occurred in a circumscribed rural area of Northern Germany. Both children had increased dietary copper exposure. The search for additional cases of what appeared to be idiopathic copper toxicosis (ICT) revealed a cluster of affected infants in this region, raising questions about the relative importance of genetic and environmental factors that are considered to be etiologic. We gathered clinical and pathologic data concerning the patients, analyzed the pedigrees of affected families, and searched for possible environmental factors contributing to the pathologic process. We encountered 8 cases of infantile liver cirrhosis in 5 families in Emsland, a circumscribed and predominantly rural area of Northern Germany; ICT was definitely proven in 2 cases. Clinical presentation and liver pathology in 6 additional cases were consistent with the diagnosis of ICT. Pedigrees of affected families revealed complex relationships with occasional consanguinity of parents, suggesting autosomal recessive inheritance. The households were served by private wells with water of low pH flowing through copper pipes, suggesting the possibility of increased alimentary copper exposure. These findings support earlier conclusions that ICT develops when an infant with a genetic predisposition is exposed to a copper-enriched diet.