Forty cats with left ventricular hypertrophic disease had blood pressure evaluated indirectly by Doppler-shift sphygmomanometry. Disease categories included hyperthyroidism, chronic renal insufficiency and hypertrophic cardiomyopathy unrelated to either of the first two disorders. Nineteen (47-5 per cent) of the 40 cats had systemic hypertension, nine had high systolic blood pressure only, 10 had high systolic and diastolic blood pressure, and none had only isolated diastolic hypertension. Blood pressure did not correlate with the degree of left ventricular thickness. The results of this study suggest a high prevalence of both left ventricular hypertrophy and systemic hypertension. Cause and effect relationships require further evaluation.