Invasive infections because of opportunistic yeasts and moulds have contributed significantly to the morbidity and mortality associated with potentially curative treatment for haematological malignancies. Many risk factors have been identified that permit the clinician to predict the likelihood of these infections. The diagnostic process involves maintaining a high index of suspicion based upon an understanding of the clinical circumstances under which invasive fungal infections occur, of the spectrum of fungal syndromes, and of the advantages and limitations of diagnostic testing strategies now available. Treatment strategies may be categorized as prophylactic, pre-emptive, empiric, or directed based upon the circumstances. The therapeutic options have increased in recent years but are not applicable to all clinical circumstances. These considerations are discussed.