Costello syndrome (CS) is a rare member of the group of neuro-cardio-facio-cutaneous diseases known as RASopathies. CS involves characteristic dysmorphic craniofacial features, cardiac defects, and increased cancer susceptibility, depending on the heterozygous activating germline mutations in HRAS. Polyhydramnios and high birth weight are the most common presentations in the perinatal and neonatal periods; while poor postnatal growth, short stature, and failure to thrive are significant issues in infancy. Possible mechanisms of short stature in CS include GH deficiency and feeding difficulties. Only a few reported cases of CS with GH deficiency exist in literature. Here, we describe the 5-yr follow-up of a CS patient with complete GH deficiency treated with recombinant human GH (rhGH) from the age of four years. No significant adverse events regarding progression of hypertrophic cardiomyopathy and tumor development were observed. She has been responsive to treatment with improved growth velocity and height standard deviation scores. She is still under continuous monitoring for concerns on the possible development of cardiac events and malignancies. This case indicated that rhGH therapy is effective for improving the height and growth velocity of CS patients with GH deficiency under close cardiac and oncological monitoring.