Objective: Clinical observations over time of adults with growth hormone (GH) deficiency (GHD) have indicated a shift in patient characteristics at diagnosis. The objective of this study was to compare baseline characteristics of patients diagnosed with adult-onset GHD naive to GH replacement during t hree study periods (1994-1999 (P1), 2000-2004 (P2), and 2005-2012 (P3)) using the KIMS (Pfizer's International Metab olic) database. Methods: Data were retrieved for a total of 6069 patients with adult-on set GHD from six countries (Belgium, Germany, Netherlands, Spain, Sweden, and UK): P1 (n = 1705), P2 (n = 2397), and P3 (n = 1967). Results: The proportions of patients with pituitary/hypothalamic tumors and patients with multiple pituitary hormone deficiencies decreased per entry year period, while the proporti ons with hypertension and diabetes increased. The lag time from diagnosis of pituitary disease to start of GH treatme nt decreased by 2.9 years over the entry year periods. IGF-1 increased by 0.1 standard deviation score per entry year period. Maximum GH following various stimulation tests, BMI, and waist circumference increased. The use of radio therapy, glucocorticoid replacement doses, and the proportion of women >50 years on estrogen replacement therapy decreased. The effects of 1 year of GH replacement were similar over the entry year periods despite changes in the patients' baseline characteristics. An expected increase in fasting blood glucose was seen after 1 year of GH treatment. Conclusions: The degree of confirmed GHD became less pronounced and more pat ients with co-morbidities and diabetes were considered for GH replacement therapy, possibly r eflecting increased knowledge and confidence in GH therapy gained with time.