Zygomycosis is an invasive and increasingly emerging life-threatening infection. Diabetes is the most common risk factor; however, zygomycosis has increased among patients with haematologic malignancy, which is now the second most common risk factor with an incidence of 16%. Rapid diagnosis and treatment are essential for patient survival. In the Danish literature, only a few cases have been reported. We present two cases of zygomycosis, both with a fatal outcome, and we discuss the pathogenesis and treatment of invasive zygomycosis.