Bacterial kidney disease is a systemic, slowly progressing, often chronic disease of wild and cultured salmonids that manifests predominately as white nodular lesions in the kidney and sometimes also in the spleen and liver. The kidney is the organ that is most commonly affected, although lesions may also be present in the heart, spleen, liver, gill and muscle. In advanced cases, most of the renal tissue may be destroyed affecting both excretory and hematopoietic functions. The renal lesions are mainly interstitial with multifocal to regionally extensive necrosis and mononuclear inflammation that may also extend to the glomeruli and surrounding tubules. Presumptive diagnosis is based on lesions and bacterial cultures. Confirmation of diagnosis is via immunological or molecular methods. Diagnosis of the condition is by the identification of the adult monogeneans and eggs on wet mount preparations of the renal tissue.