Introduction. Legionella is a frequent cause of bacterial pneumonia in patients with AIDS. While multiple organisms have been associated with cavitary pneumonia in this population, Legionella has not. Clinical Case. A middle-aged woman with HIV-AIDS and severely depressed CD-4 count presented with one month of progressively worsening productive cough and dyspnea. Serial imaging showed focal consolidations which multiplied and cavitated over the subsequent days. Legionella urine antigen was positive, and appropriate treatment was continued for 3 weeks total. The patient recovered quickly, and follow-up imaging 8 weeks later showed near-resolution of all lesions. Discussion. Cavitary pneumonia secondary to Legionella has been seldom described, traditionally in the context of immunosuppressive therapy. Patients with AIDS and severely depressed CD4 counts have significantly compromised cell-mediated immunity. This case highlights the importance of consideration for legionellosis in rapidly progressing cavitary pneumonia, especially in patients with severely compromised cell-mediated immunity, including those with HIV-AIDS.