Copyright © 2014 by the Endocrine Society. Context: Previous studies showed improvement in impaired quality of life (QoL) in adult patients with growth hormone (GH) deficiency (GHD) who were treated with GH; improvement was sustained over a few years after GH therapy. Objective: To evaluate the QoL over 10 years. Design: This was a prospective observational study. Setting: The study was conducted in clinical practice. Patients: 1436 adult patients with adult-onset (AO) GHD (mean age [standard deviation (SD)]: 49.0 [12.2] years; 49% female) and 96 with childhood-onset (CO) GHD (31.3 [10.0] years; 60% female) (total N = 1532). Intervention: GH therapy. Main Outcome Measures: QoL was measured by Questions on Life Satisfaction-Hypopituitarism (QLS-H) in countries where validated questionnaires and normative data for calculation of Z-scores were available. Change in QoL was tested by Student's t test and predicted by mixed-model repeated measures (MMRM) analysis. Results: At study entry, patients had diminished QoL Z-scores (mean [SD] AO, -1.55 [1.69]; CO -0.98 [1.32]). The largest QoL improvements were in the first year: mean (SD) increase 0.77 (1.37) for AO (P < .001) and 0.50 (1.37) for CO (P < .001). The initial improvement from study entry remained statistically significant throughout 10 years for AO and in years 1 to 4, 6, and 7 for CO (P < .05). MMRM analysis predicted a greater QoL improvement in those who were not depressed, lived in Europe, had poorer Z-scores at entry, had lower body mass index at entry, and had no impaired vision. Conclusion: These data suggest that GH replacement provides sustained improvement in QLS-H scores toward normality for up to 10 years.