A 6-mo-old female Chihuahua was presented with recurrent episodes of hypoglycemia and collapse. Physical examination revealed proportionate dwarfism, retained puppy hair coat, retained deciduous teeth, and open fontanelles. Routine blood tests revealed hypoglycemia, thrombocytosis, hypoproteinemia, and elevated alkaline phosphatase activity. The urinalysis, radiographs, and ultrasonographs were unremarkable. Endocrine testing revealed that insulin-like growth factor 1 was below the detection limit; concentrations of total thyroxine, baseline cortisol, and cortisol stimulated by tetracosactide acetate were within their reference intervals. The pituitary gland showed no organic abnormalities on magnetic resonance imaging. For definitive diagnosis, we conducted the stimulation test for growth hormone (GH) release and diagnosed isolated GH deficiency. Genetic investigation revealed that the present case had 4 point mutations in intronic regions and a 6-bp deletion in exon 5 of GH1. The bioinformatics tool PROVEAN algorithm predicted that the deletion in exon 5 could be deleterious to the function of GH1.