For most opportunistic mycoses no optimum duration of antifungal therapy has been defined. Although a long course of therapy is prudent, especially for mycelial fungal infections, excessively and unnecessarily extended courses of treatment incur a risk of toxicity and the expense of the therapeutic regimen. On the basis of existing reports on the pathogenesis and the effect of duration of therapy and other variables on outcome and response rate in fungal infections, this review proposes guidelines that may facilitate a rational approach to decision-making about the duration of antifungal therapy.