Objective: to study risk factors for invasive aspergillosis (IA), its etiology, clinical manifestations, and treatment efficiency in patients with rheumatic diseases (RD).Patients and methods. The first study of proven and probable IA (EORT/MSGERC, 2019) was conducted in 18 patients with RD, who accounted for 3% of all adult IA patients (n=699) included in the 1998–2020 registry of the Department of Clinical Mycology, Allergology, and Immunology, I.I. Mechnikov North-Western State Medical University (Group 1). This group comprised 56% women; the median age was 59 [21; 75] years. Group 2 (a comparison group) included 610 adult hematology patients with IA (median age, 45 [18; 79] years; 42% women). A prospective case-control study was conducted to identify risk factors for IA in patients with RD: 36 rheumatic patients without IA (median age, 58 (18–79) years; 61% women) (a control group).Results and discussion. Patients with RD were found to often develop IA in the presence of anti-neutrophilic cytoplasmic antibody-associated vasculitis (granulomatosis with polyangiitis and microscopic polyangiitis) and systemic lupus erythematosus (50 and 16%, respectively). It was shown for the first time that the likelihood of IA in patients with RD increases with prolonged (median 14 days) lymphocytopenia during RD treatment (odds ratio 13.0; 95% confidence interval, 3.3–50.3). The main causative agents of IA were A. fumigatus (50%) and A. niger (29%). IA was more severe in Group 1 than in Group 2: in the resuscitation and intensive care units, there were 44 and 18%, respectively (p=0.01). Group 1 versus Group 2 more frequently had respiratory failure (61 and 37%, respectively; p=0.03), hemoptysis (28 and 7%; p=0.0001), chest pain (17 and 7%; p=0.04), and cardiac involvement (11 and 1%; p=0.0001), and less frequently had fever (67 and 85%; p=0.01). The common site of IA was the lung (83%); the characteristic feature detected by computed tomography (CT) is pulmonary cavitation (44%). Antifungal therapy was used in 89% of Group 1 patients; the overall 12-week survival was 69%.Conclusion. In patients with RD, it is difficult to differentiate between the progression of the underlying disease, adverse drug reactions, infectious complications, or a combination of these disorders due to the similarity of their clinical manifestations. When RD patients with infectious syndrome and respiratory failure develop prolonged lymphocytopenia during combination therapy, AI should be suspected and lung CT, bronchoscopy, and mycological examination of the material obtained by bronchoalveolar lavage be done.