To evaluate the efficacy and safety of itraconazole oral solution for preventing fungal infections, a randomized, placebo-controlled, double-blind, multicenter trial was conducted: 405 neutropenic patients with hematologic malignancies were randomly assigned to receive either itraconazole, 2.5 mg/kg every 12 hours (201 patients), or placebo (204 patients). Proven and suspected deep fungal infection occurred in 24% of itraconazole recipients and in 33% of placebo recipients, a difference of 9 percentage points (95% confidence interval [CI], 0.6% to 22.5%; P = .035). Fungemia due to Candida species was documented in 0.5% of itraconazole recipients and in 4% of placebo recipients, a difference of 3.5 percentage points (95% CI, 0.5% to 6%; P = .01). Deaths due to candidemia occurred in none of the itraconazole recipients compared with 4 placebo recipients, a difference of 2 percentage points (95% CI, 0.05% to 4%; P = .06). Aspergillus infection was documented in four itraconazole recipients (one death) and one placebo recipient (one death). Side effects causing drug interruption occurred in 18% of itraconazole recipients and 13% of placebo recipients. Itraconazole oral solution was well-tolerated and effectively prevented proven and suspected deep fungal infection as well as systemic infection and death due to Candida species.