['We studied whether the severity of GH deficiency (GHD) defined as i) GH-peak on stimulation tests (insulin tolerance test (ITT), arginine, and glucagon), ii) number of additional pituitary deficits, or iii) baseline IGF1 SDS could impact the response to GH treatment. We further explored whether iv) IGF1 SDS after 24 months of GH replacement or v) ΔIGF1 SDS from baseline to 24 months was related to the phenotypic response to GH treatment. DESIGN, PATIENTS, AND MEASUREMENTS: The patient cohort (n=1752; 50% women) was obtained from KIMS (Pfizer International Metabolic Database). The patients were divided into three groups of approximately equal size (tertiles) according to the stimulated GH-peak values and baseline IGF1 SDS and were studied at baseline, 12, and 24 months of GH therapy.', 'Lower baseline IGF1 SDS predicted better response in weight, BMI, total cholesterol, and triglycerides, while IGF1 SDS after 24 months was associated with reduction in waist/hip ratio, total cholesterol, and improved quality of life (QoL). Age-correlated negatively with the response in body weight, BMI, waist, IGF1 SDS, and total and LDL-cholesterol. Response in weight and BMI was greater in men than in women, whereas women showed greater improvement in QoL than men. Patients with more severe GHD as assessed by lower GH-peaks and more pituitary hormone deficiencies had a greater increase in IGF1 SDS. The increase in IGF1 SDS was associated with a reduction in waist/hip ratio and an increase in weight, BMI, and triglycerides. There was no correlation with other lipids, blood pressure, or glucose.'] Is response to GH treatment in adult GH deficiency predicted by gender , age , and IGF1 SDS but not by stimulated GH-peak?