Invasive fungal infections (IFIs) are a leading cause of morbidity and mortality in cancer patients admitted to intensive care units (ICUs). The patients typically exhibit multiple risk factors for IFIs, including barrier injury due to surgery, drains and catheters, effects from chemotherapy, neutropenia, corticosteroid exposure, renal and/or hepatic dysfunction, intra-abdominal surgery, and total parenteral nutrition (TPN). Candida remains the most common etiology of IFI. Prompt treatment, control of the sources of infection (e.g., removal of central venous catheters and drainage of abscesses), and prompt and appropriate selection, including dosing, of antifungals remain keys to survival in invasive candidiasis. Although fluconazole has been replaced by echinocandins as the first-line agent for candidemia, knowledge of prior antifungal exposure and hospital epidemiology is essential to appropriate antifungal selection. The most common mold isolated in oncologic ICUs is Aspergillus. Aggressive anti-mold prophylaxis has resulted in breakthrough infections with uncommon and resistant molds, such as Fusarium, Lomentospora, and Mucorales, which are increasingly more common. Diagnosis of IFIs requires high index of suspicion and art of risk stratification for IFI risk. New diagnostic methods, including fungal biomarkers, mass spectrometry (MALDI-TOF), and magnetic resonance (T2MR), have led to more rapid diagnosis, but many questions remain unanswered regarding real-world use of these tools in highly complex patient populations in cancer center ICUs. Despite improvements in therapeutic and diagnostic modalities, the activity of underlying disease and comorbidities are the most important drivers for outcome.