Invasive pulmonary aspergillosis (IPA) is a frequently fatal complication in patients with acute leukaemia. Because diagnosis is still difficult, non-invasive diagnostic criteria were recently proposed by MSG/IFICG/EORTC for study purposes. We have analysed their usefulness in the clinical management of acute leukaemic patients with pulmonary infiltrates. Twenty-seven infiltrates developed during 174 chemotherapy cycles given to 50 consecutive patients. According to diagnostic criteria, IPA was diagnosed in 42% of patients and 77.8% of pulmonary infiltrates. AML diagnosis and the first induction cycle were significant risk factors. “Proven” IPA was rare, occurring in one patient (2%). The diagnosis of “probable” IPA was made in seven patients (14%) and was strongly supported by the significant association of characteristic radiological lesions (“major” clinical criterion) with the positivity of one microbiological criterion (P = 0.026). Conversely, “possible” IPA was frequent (26%) because its pertinent diagnostic criteria were fulfilled in 48.1% of pulmonary infiltrates. However, in 84.6% of cases, the diagnosis of “possible IPA” aspecifically derived from the association of two conditions, a new pulmonary infiltrate with symptoms of lower respiratory tract infection (“minor clinical criterion”), together with the definition of “susceptible” host, which applied to 100% of our leukaemic patients. We conclude that, according to MSG/IFICG/EORTC criteria, a high number of pulmonary infiltrates would be diagnosed as IPA, but only a diagnosis of “proven/probable” IPA should be considered reliable in the clinical management of suspected IPA.