An open-label extension study to evaluate the safety of long-term twice-monthly administration of somavaratan in adults with Growth Hormone Deficiency (GHD). This multicenter study is open to subjects completing a Versartis adult GHD study as well as approximately 40 new somavaratan naïve subjects (either rhGH treatment naïve or currently receiving daily rhGH therapy). All subjects will receive twice-monthly (every 15 days ± 2 days) subcutaneous (SC) somavaratan. Doses will be titrated to each subject's individual IGF-I responses based on the IGF-I level 7 days post-dose until a maintenance dose is achieved. Subjects receiving somavaratan in a previous somavaratan study will have their dose decreased by half (minimum dose of 20 mg, 40 mg for women on estrogen, rounded down to the nearest even number) and will be titrated per the Dose Titration Plan. New subjects enrolling in this study will be assigned to one of two cohorts based on sensitivity to rhGH and titrated per the Dose Titration Plan.