OBJECTIVES: We tested the hypothesis that twice weekly prophylactic dosing of fluconazole prevents invasive candidiasis without promoting resistant Candida species in high-risk, preterm infants. STUDY DESIGN: We compared our previous dosing schedule (Group A) to a less frequent dosing schedule of twice a week (Group B) of fluconazole prophylaxis for up to 6 weeks in a prospective, randomized, double-blind clinical trial in preterm infants weighing <1000 grams at birth and with an endotracheal tube and/or central vascular catheter over a 24-month period. Weekly surveillance cultures were obtained on study patients. RESULTS: Candida colonization was documented in 5 (12%) of 41 Group A and in 4 (10%) of 40 Group B infants. Candida sepsis developed in two (5%) of Group A and one (3%) of Group B infants (risk difference, -0.02; 95% confidence interval, -0.14-0.10; P=.68). All fungal isolates remained sensitive to fluconazole, and no drug side effects were documented. CONCLUSIONS: Twice weekly dosing of prophylactic fluconazole can decrease Candida colonization and invasive infection, cost, and patient exposure in high-risk, preterm infants weighing <1000 grams at birth. We speculate that lower and less frequent dosing may delay or prevent the emergence of antifungal resistance.