BACKGROUND: Tropical spastic paraparesis or HTLV-I-associated myelopathy (TSP/HAM) is a chronic neurological disease etiologically linked to human T-cell lymphotropic virus type I (HTLV-I). OBJECTIVE: to serologically confirm infection by and isolation of HTLV-I from the peripheral blood mononuclear cells from a patient who presented with a clinical picture similar to that of tropical spastic paraparesis. METHODS: peripheral blood mononuclear cells were co-cultured for 35 days. Viral detection by membrane-specific immunofluorescence and polymerase chain reaction of genes tax, pol and gag were performed. RESULTS: The presence of antibody to human T cell lymphotropic virus type I in serum was confirmed. Indirect immunofluorescence in the sequential monitoring made it possible to observe an increase of the number of positive cells whereas proviral DNA was detected in the peripheral blood mononuclear cells. CONCLUSIONS: these results support the evidence of viral isolation and confirmed, for first time in Cuba, the association between HTLV-I and TSP.