Aspergillus species remains an important cause of morbidity and mortality in immunosuppressed patients. The following case report presents a 56-year-old HIV-infected patient on successful combined antiretroviral therapy (cART), who was diagnosed with non-small cell lung cancer in November 2015 and invasive aspergillosis in January 2016. At that time, we noticed a sudden decrease of his CD4+ count from 758 cells/μl in October 2015 to 48 cells/μl in January 2016. It was probably not a result of HIV infection, because viral load had been undetectable, and the CD4+ count had remained > 500 cells/μl for many years. It is more likely that the patient’s severe lymphopenia was caused by metastatic cancer and the treatment (radiotherapy) that had been applied. There is data showing that a significant decrease of the CD4+ count is a frequent side effect in patients following treatment with radiation and chemotherapy for newly diagnosed solid tumors, regardless of histopathology and the type of chemotherapy. Both advanced AIDS and immune deficiencies connected with solid organ tumors are risk factors for invasive pulmonary aspergillosis and as the case described illustrates, these two medical conditions are often connected with severe lym-phopenia. The question that arises is whether severe lymphopenia constitutes an independent risk factor for invasive pulmonary aspergillosis.