Invasive pulmonary aspergillosis (IPA) is an important cause of morbidity and mortality in neutropenic, nonneutropenic, and other immunocompromised patients. We therefore compared the patterns of infection and inflammation among 3 cohorts of immunocompromised patients with profound neutropenia, nonneutropenic immunosuppression, and hematopoietic stem cell transplantation. Lesions of IPA in neutropenic patients and hematopoietic stem cell transplant (HSCT) recipients were similar and consisted predominantly of angioinvasion and intraalveolar hemorrhage. The frequency of these histologic findings in neutropenic patients and HSCT recipients differed significantly from those of nonneutropenic patients (P < .05). It is noteworthy that even if HSCT recipients have normal peripheral blood neutrophil counts, there may be no influx into sites of infection. In the nonneutropenic cohort, lesions of IPA consisted mainly of neutrophilic and monocytic infiltrates and inflammatory necrosis. Thus, the status of innate host defenses contributes significantly to the histologic patterns observed in IPA.