We encountered a 91-year-old patient with acromegalic features. The serum levels of growth hormone (GH) and insulin-like growth factor-I (IGF-I) were increased to 23.3ng/ml and to 268ng/ml, respectively. Both thyrotropin-releasing hormone and luteinizing hormone-releasing hormone tests demonstrated a 2-3 fold increase in the serum GH level. Magnetic resonance imaging disclosed a pituitary mass in the enlarged sella. The patient was diagnosed as having acromegaly due to overproduction of GH from a pituitary tumor. She manifested cardiac hypertrophy with severe aortic stenosis and mild hypertension, but without diabetes mellitus. After the administration of octreotide subcutaneously at a dose of 25 to 50μg daily for 20 days, the serum GH level increased transiently but decreased rapidly to approximately half the initial level, and suppression of the GH level persisted thereafter for over 2.5 months. This patient seems to be the oldest patient with acromegaly among those reported in Japan.