Zygomycoses are rare invasive mould infections which mainly occur in immunocompromised patients, especially during prolonged neutropenia. The high mortality rate is due to a high failure rate of both intravital diagnosis and treatment. Exact diagnosis requires microscopic examination and proof by culture. The treatment consists of amphotericin B and surgical debridement. We report four recent cases of zygomycosis among 89 patients with intensively treated acute leukaemia at our institution. Three cases were breakthrough infections since the patients were under voriconazole treatment prior to diagnosis of zygomycosis. Only one patient had premortal diagnosis (paranasal sinus infection) and showed clinical response with amphotericin B and surgical debridement. A review of the literature of these emerging fungal infections is given and is focused on patients with acute leukaemia. In addition, the importance of autopsy as a tool for quality control and epidemiological studies is pointed out.