About 70% of AIDS-associated lymphomas are Non-Hodgkin lymphomas (NHL). Primary soft tissue NHL is very rare and accounts only the 0.1% of the cases. Generally, NHL of the soft tissue presents as large subcutaneous masses as primary clinical manifestation of neoplasm disease. Initially the mass lesions have a fast growing, with or without evidence of nodal or skin involvement. Here, we describe a patient with AIDS who developed a primary NHL of the soft tissue, presenting as a large subaxillary thoracic mass. Patient was successfully treated with highly active antiretroviral therapy plus chemotherapy with a prolonged survival and immune reconstitution.