Twenty-four cats with spontaneous systemic hypertension were retrospectively studied. Blood pressure (BP) was measured indirectly by the Doppler technique in 17 cats (mean systolic 219.4 +/- 43.2 mm Hg) and directly by femoral arterial puncture in 15 cats (mean systolic/diastolic 233.2 +/- 40.9/148.1 +/- 28.7 mm Hg). All cats had bilateral retinal hemorrhages and/or detachments. Twenty cats presented because of blindness. Other presenting signs included polyuria/polydipsia, weight loss, neurological signs, and/or epistaxis. Diagnostic tests were performed to determine the presence and the cause of any secondary organ damage. Common findings included retinal hemorrhages/detachments, low-grade systolic murmurs, cardiomegaly with left ventricular hypertrophy (LVH), small kidneys, mild azotemia, and urine specific gravity < or = 1.020. Only 3 cats had hyperthyroidism. One cat was transiently diabetic. Necropsies on 2 cats with neurological signs showed nephrosclerosis, arteriosclerosis, and multifocal cerebral hemorrhages. Twenty cats were treated with diuretics, beta-adrenergic antagonists, and/or an angiotensin converting enzyme (ACE) inhibitor. One cat was treated with methimazole only, and 1 was treated with insulin transiently. The median survival of the 24 cats was 18 months. Response to therapy did not appear to have an impact on survival time.