We report here 3 cases of aspergillus sinusitis in patients with AIDS and the 1st fully described case, to our knowledge, of sinusitis associated with Pseudallescheria boydii in a patient with AIDS. We review the microbiology and pathology of fungal sinusitis in patients with AIDS and the morphologic and clinical features and treatment of P. boydii infection and aspergillus sinusitis. Fungal sinusitis in patients with HIV or AIDS generally occurs later in the course of primary disease with low CD4+ lymphocyte counts (< 50/mm3), unlike bacterial sinusitis which may occur at any time. Differentiation between invasive and noninvasive forms is likely not important, in contrast to fungal sinusitis in noncompromised patients. The number of cases is likely to increase as the number of patients with AIDS increases, patients survive longer, and other opportunistic infections are prevented or treated. Causative agents are likely to be resistant to fluconazole, which is in widespread use. Aspergillus sinusitis in patients with HIV or AIDS occurs in both those with and without traditional risk factors. Fungal sinusitis may present vexing management problems and be relentlessly progressive in the face of therapy. Ideal therapy has yet to be defined but an early combined surgical and medical approach in these compromised patients is preferred.