We examined the birthweight-, gender- and race-specific incidence as well as the biodemographic and clinical correlates of necrotising enterocolitis (NEC) in a well-defined six-county perinatal region in upstate New York. We conducted a retrospective, 8-year population-based survey to identify all cases of proven NEC (modified Bell stage II and above) in the area's regional neonatal intensive care unit (NICU). The denominator used to calculate the incidence was obtained from the Statewide Planning Research Cooperative System. Incidence was expressed as cases per 1000 live births. A total of 85 documented cases of proven NEC was identified in a six-county perinatal region that experienced 117 892 live births during the 8-year period. The average annual incidence was 0.72 cases per 1000 live births [95% CI 0.57, 0.87 per 1000 live births]. The highest incidence of NEC occurred among infants weighing 750-1000 g at birth and declined with increasing birthweight. The urban county had a 1.53 times higher risk of NEC than rural counties [95% CI 0.9, 2.6]. The overall incidence of NEC for non-Hispanic blacks was significantly greater than that for non- Hispanic whites (2.2 vs. 0.5 cases per 1000 live births, P = 0.00). The differences remained statistically significant even after correction for birthweight. Most cases (93%) in this series were preterm (gestational age <37 weeks). Only two patients were never fed before the diagnosis of NEC was confirmed. Positive blood cultures were documented in 27% of the cases with a predominance of Gram-negative enteric micro-organisms. NEC remains an important health problem especially for preterm infants and the non-Hispanic black population.