In many short-stature patients with human T-lymphotrophic virus type I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), signs and symptoms were manifested during childhood. Successive investigations revealed 12 of 14 short-stature patients with pseudohypoparathyroidism (PHP) from the findings of short metacarpi, parathyroid hormone infusion test, immunoblotting of erythrocyte membrane, or lymphocytic Northern blotting of Gsalpha. Patients with PHP probably showed HAM/TSP based on their modified immunologic status. Human T-lymphotrophic virus type I infection did not induce PHP, but PHP may be a risk factor for the occurrence of HAM/TSP.