Adult T-cell leukemia/lymphoma belongs to the group of mature T-cell malignancies according to the WHO classification. It constitutes a rare entity and has a strong association with infection by human T-lymphotropic virus 1. In Uruguay, this viral infection is very infrequent and, to our knowledge, no case of adult T-cell leukemia/lymphoma has been previously reported. We describe the case of a woman, immigrant from Peru, who presented with persistent lymphocytosis, intestinal parasitic diseases, and skin involvement. The diagnosis was delayed and the patient died before initiating oncological treatment. We therefore emphasize the relevance of an early clinical suspicion and serology for this virus, especially in patients coming from endemic countries like Peru.