Objective: Colonization by Candida spp is a major risk factor for development of fungal sepsis, but little is known about the variables associated with progression to invasive disease in already colonized neonates. We investigated such variables in a large number of colonized preterm neonates in an NICU., Setting: This study was conducted in the Department of Neonatology and the NICU at Sant'Anna Hospital in Torino, Italy., Design and Patients: A database search of clinical charts and weekly surveillance cultures was used to identify all neonates with birth weights < 1500 g (very low birth weight) who were admitted to our NICU during 1998-2005 and were colonized (> or = 1 site) by Candida spp during their stay, as well as infants with invasive fungal infection. The association between a number of factors with progression to invasive fungal infection was evaluated. Those shown to be significantly associated by univariate analysis were cross-checked by logistic regression., Results: Colonization occurred in 201 infants (32.1% of very low birth weight admitted neonates), and invasive fungal infection occurred in 51 (8.1%) of them, with an overall progression rate of 0.25. At univariate analysis, 10 factors (namely low birth weight, low gestational age, use of third-generation cephalosporins, endotracheal intubation, duration of stay in the NICU, bacterial sepsis, colonization of central venous catheter, of endotracheal tube, of gastric aspirate, or in > or = 3 [multiple] sites) were associated with an increased risk of progression, whereas prophylaxis with fluconazole was associated to a decreased risk. After logistic regression, only colonization of central venous catheter and colonization in multiple sites remained significantly associated with invasive fungal infection. Fluconazole prophylaxis remained an independent protective factor., Conclusions: Central venous catheter colonization and multiple-site colonization are independent risk factors and predictors of progression to fungal sepsis in preterm very low birth weight neonates colonized by Candida spp during their stay in the NICU. Fluconazole prophylaxis is an independent protective factor. These findings can be used to improve the surveillance, prophylaxis, or preemptive measures in neonates at high risk.