Empirical antifungal therapy is widely used in high-risk neutropenic hematology patients with fever persisting for more than 4 days. This clinical trial assessed whether immediate empirical therapy with voriconazole could lower the rates of invasive fungal infections (IFIs) compared with this approach. In a double-blind, placebo-controlled, multicenter study, patients with acute leukemia undergoing chemotherapy or allogeneic hematopoietic stem cell transplantation (HSCT) recipients were randomized to broad-spectrum antibacterial therapy plus voriconazole (immediate) or placebo (deferred) after the onset of neutropenic fever. If fever persisted for 96 h, patients were switched to open-label intravenous voriconazole; oral treatment was permitted after 96 h. The primary endpoint was the rate of proven/probable IFIs between Days 2 and 28 after fever onset in the modified intent-to-treat (mITT) complete-case population. One hundred and forty-seven patients were randomized to immediate (n = 81) or deferred (n = 66) voriconazole. In the mITT population, six patients in the immediate group and nine in the deferred group developed proven/probable IFI between Days 2 and 28 (p = 0.258). The safety profiles were similar in both groups. While immediate empirical therapy with voriconazole appears to be safe in febrile neutropenic high-risk patients, it was not associated with a significant reduction in IFIs compared with therapy deferred for 96 h after fever onset.