Tropical spastic paraparesis or human T-lymphotropic virus type I (HTLV-I)-associated myelopathy is a degenerative encephalomyelopathy with pyramidal tract dysfunction affecting the lower extremities. It is associated with HTLV-I infection and found primarily in the Caribbean region and in southwestern Japan. Five cases of tropical spastic paraparesis (or HTLV-I-associated myelopathy) in Hawaii are reported. All five patients were born in Hawaii; four are women. Each of the patients has parents who were from HTLV-I-endemic areas of Japan. Two of these patients had serum antibodies to HTLV-I. Five of six of the spouses and children of the seropositive patients were also seropositive. Viral cultures of lymphocytes from both seropositive patients and two of the three seropositive children were positive for HTLV-I. None of the five patients had a history of antecedent blood transfusion, multiple sexual partners, or intravenous drug use. There is no evidence of adult T-cell leukemia or lymphoma in any of the patients or their families. Given the increasing seroprevalence of HTLV-I in the United States, clinicians need to be alert to new cases of this disorder.