Objective: Adherence to treatment regimen is a key factor in the success of Growth Hormone (GH) therapy. Our objective was to assess the long time adherence to treatment in a large cohort of patients. Design: It is a retrospective study. The data was collected from a single central computerized data center well maintained and checked for quality. All patient aged 1–16 years, treated with GH during 2006–2015 for >2 years, who were insured by “Clalit” Health Maintenance Organization. Adherence was measured by the number of months of pharmacy purchased GH annually: good (11−12), moderate (7–10), and poor (<7) months per year. Results: 2263 patients (59% males) were treated for >2 years. Mean age at treatment initiation was 8.3 ± 3.6 years, 74% were secular Jews, 6.8% ultra-religious Jews and 18.9% of Arab origin. Only 30% of patients had good adherence to GH therapy. Patients who started treatment before age 8 years had poorest adherence rate. No association was found between adherence to GH therapy and gender or socioeconomic status. In a multivariate analysis (gender, age groups, ethnicity and clinic SES) we found the ultra-religious population had higher risk for non adherence (OR 2.16, CI 95% 1.46–3.19). The poorest adherence by age was in the youngest patients. In patients treated for >5 years (n = 668), adherence rate declined slightly over the years. Conclusions: Long term adherence to GH therapy is suboptimal. Measures for improving adherence especially among younger and ultra- religious patients are needed.