A 26-year-old male seropositive for human immunodeficiency virus (HIV) infection presented with atypical Hodgkin's disease. Subsequently, synchronous, aggressive non-Hodgkin's lymphoma was identified in this patient. Atypical Hodgkin's disease appears to be an opportunistic neoplasm in patients seropositive for HIV infections and should be considered as an indicator disease for the definition of acquired immunodeficiency syndrome (AIDS).