Severe infections caused by non-albicans Candida species are being increasingly reported among infants in neonatal intensive care units. To assess relative severity, mortality rates for C. albicans (CA) and C. parapsilosis (CP) infections in one neonatal intensive care unit from 1980 to 1990 were compared. Invasive candidiasis was defined as Candida recovery from a normally sterile body fluid or site with clinical signs of infection. Invasive candidiasis was diagnosed and systemic antifungal therapy initiated in 45 infants, 29 with CA and 16 with CP. No differences were found between CA and CP for birth weight, gestational age, age or weight at onset, presence of necrotizing enterocolitis, gastrointestinal or genitourinary anomalies, death (all causes), prior incidence or duration of antibiotics, parenteral nutrition, steroids or endotracheal intubation. Candida infection as the cause of death was more frequent with CA than CP (7 of 29 vs. 0 of 16; P = 0.034). Infants with CA were more likely to have antecedent thrush (P = 0.007) and perineal Candida dermatitis (P less than 0.02); those with CP were more likely to have vascular catheters at the time of positive culture (P less than 0.02). Though both pathogens occur in similar neonatal intensive care unit infants and can cause severe disease, CA appears more likely to result in death than CP.