, two episodes of Candida tropicalis fungemia occurred in the Aristotle University neonatal intensive care unit (ICU). To investigate this uncommon event, a prospective study of fungal colonization and infection was conducted. From December 1998 to December 1999, surveillance cultures of the oral cavities and perinea of the 593 of the 781 neonates admitted to the neonatal ICU who were expected to stay for >7 days were performed. Potential environmental reservoirs and possible risk factors for acquisition of C. tropicalis were searched for. Molecular epidemiologic studies by two methods of restriction fragment length polymorphism analysis and two methods of random amplified polymorphic DNA analysis were performed. Seventy-two neonates were colonized by yeasts (12.1%), of which 30 were colonized by Candida albicans, 17 were colonized by C. tropicalis, and 5 were colonized by Candida parapsilosis. From December 1998 to December 1999, 10 cases of fungemia occurred; 6 were due to C. parapsilosis, 2 were due to C. tropicalis, 1 was due to Candida glabrata, and 1 was due to Trichosporon asahii (12.8/1,000 admissions). Fungemia occurred more frequently in colonized than in noncolonized neonates (P < 0.0001). Genetic analysis of 11 colonization isolates and the two late blood isolates of C. tropicalis demonstrated two genotypes. One blood isolate and nine colonization isolates belonged to a single type. The fungemia/colonization ratio of C. parapsilosis (3/5) was greater than that of C. tropicalis (2/17, P ؍ 0.05), other non-C. albicans Candida spp. (1/11, P ؍ 0.02), or C. albicans (0/27, P ؍ 0.05). Extensive environmental cultures revealed no common source of C. tropicalis or C. parapsilosis. There was neither prophylactic use of azoles nor other risk factors found for acquisition of C. tropicalis except for total parenteral nutrition. A substantial risk of colonization by non-C. albicans Candida spp. in the neonatal ICU may lead to a preponderance of C. tropicalis as a significant cause of neonatal fungemia.Candida spp. are common causes of nosocomial invasive infections in neonatal intensive care units (ICUs). Although Candida albicans has historically been the most frequently isolated species, infections caused by non-C. albicans Candida spp. have been diagnosed with increased frequency in recent years (14,17). In particular, Candida parapsilosis has become the predominant fungal pathogen in many neonatal ICUs (11,14,17). Moreover, recent studies have shown that C. parapsilosis is often a cause of clusters and common-source outbreaks (12, 29).In contrast, little is known about the roles of other non-C. albicans Candida spp. in neonatal ICUs (4). To our knowledge, Candida tropicalis fungemia in neonates has not been adequately described, and the significance of mucocutaneous colonization of neonates by this pathogen remains speculative.Two chronologically related unusual cases of C. tropicalis fungemia that occurred in the Aristotle University neonatal ICU prompted us to initiate a prospective study of fungal co...