Objective. To study risk factors, etiology, clinical signs and treatment outcomes of invasive aspergillosis (IA) and mucormycosis combination (IAM) in children. Materials and methods. A retrospective review of Saint-Petersburg register (1998–2021) of patients with IA was done and children with IAM were included. EORTC/MSGERG 2019 criteria were used for diagnosing and treatment results evaluation of invasive mycosis. We presented a clinical case of IAM in a child with acute lymphoblastic leukemia relapse. Results. A total of 12 children with IAM were included. They accounted 8% of all pediatric patients with invasive aspergillosis (n = 152). IAM was diagnosed in children with hematological malignancies and solid tumors from 4 to 16 years (median age – 11.5 years), mostly in girls (83%). Main risk factors of IAM were prolonged lymphopenia (75%, median 22 days) and neutropenia (67%, median 30 days) due to chemotherapy, systemic corticosteroids and/or immunosuppressive therapy, as well as HSCT. The predominant etiological agents of IA were Aspergillus niger (33%), A. nidulans (33%) and A. fumigatus (17%), of mucormycosis – Lichtheimia corymbifera (50%) and Rhizomucor spp. (50%). Based on EORTC/MSGERG 2019 criteria, «proven» mucormycosis was diagnosed in 83% of patients, «probable» – in 17%. «Probable» IA was found in 100% of patients. The most common clinical sites of IAM were the lungs (75%) and paranasal sinuses (43%), multifocal involvement was revealed in 33% of patients. Mucormycosis developed during antifungal therapy of IA in 83% of patients. Antifungal therapy of mucormycosis received 75% of patients (amphotericin B lipid complex – 89%, posaconazole – 78%, caspofungin – 33%), combined antifungal therapy – 33%, surgery – 50%; combination of surgical and antifungal treatment was used in 42% of patients. The overall 12-week survival was 77.8%. The use of combined surgical and antifungal treatment significantly improved the survival of children with IAM (p = 0.023). Conclusions. Mucormycosis was diagnosed in 8% of children with IA. IAM developed mostly in patients with hematological malignancies (83%), prolonged lymphopenia (75%) and neutropenia (67%) against the background of chemotherapy, systemic corticosteroids and/or immunosuppressive therapy, as well as HSCT. In 83% of patients mucormycosis was diagnosed during antifungal therapy for IA. The development of IAM increased overall 12-week mortality (50%). The combination of antifungal therapy with surgical treatment significantly improved prognosis of IAM (p = 0.023).