To know the longitudinal shift of blood IGF-1 of cured acromegaly, we conducted retrospective survey of changes in blood IGF-1 over two years, which has not been previously investigated. Blood IGF-1 levels were measured for longer than 2 years after TSS in 37 patients whose nadir GH during postoperative oral glucose tolerance test (OGTt) was under 1 ng/mL. Blood IGF-1 very gradually declined after three months; 230.6 (mean) ng/mL at 3-12 months, 202.3 ng/mL at 12-24 months, and 198.6 ng/mL at 24-36 months. Their SD values, calculated based on standard IGF-1 values of age- and sex-matched Japanese population, also slowly decreased after three months; 1.69 (mean) at 3-12 months, 1.23 at 12-24 months, and 1.12 at 24-36 months. Very slow decrease of the IGF-1 levels continued beyond the first several months and even the first year after TSS. The declination of values is greater than that associated with aging. This declination may be at least partially a reflection of the slow decrease and late normalization of GH secretion.