Primary hyperaldosteronism is a disease characterised by elevated aldosterone secretion by the adrenal glands. The present case series describes seven cats with primary hyperaldosteronism presented between 2002 and 2011. Common clinical signs were weakness, anorexia, cervical ventroflexion and blindness. All cats showed hypokalaemia. Blood pressure measurement in six cats revealed hypertension in five; four of the five cats were blind because of retinal detachment. Ultrasonographic examination showed unilateral adrenomegaly in six cats and normal adrenals in one. The serum aldosterone concentration exceeded the reference range in four cats. Five cats underwent unilateral adrenalectomy, which was without complications and led to normalisation of the electrolyte concentrations. Histological examination of the adrenal glands revealed adrenocortical adenoma in four cats and adrenocortical carcinoma in two; the cat with ultrasonographic normal adrenals had bilateral nodular adrenal hyperplasia.