Though correlated, birthweight (BW) and gestational age (GA) have independent effects on cognitive and neurological outcomes. Jurisdictions vary in their inclusion of these two characteristics in their list of established conditions for automatic eligibility for Early Intervention (EI) services, which may lead them to miss important high-risk groups. We evaluated the relationship between BW-GA combinations and both EI referral rates and risk of EI-diagnosed significant developmental delay in a population of New York City (NYC) births. We linked birth certificates of children born in NYC to resident mothers during 1999-2001 and surviving the first 28 days of life (n = 339,522) to EI administrative data. We calculated EI referral rates for various BW-GA categories, and used a logistic model to directly estimate the predicted risk of delay. EI referral rates of over 50% were observed in children born <1,250 g and those born <30 weeks and 1,250-1,499 g. Additionally, more than one in two children born either less than 1,250 g or <30 weeks and 1,250-1,499 g were predicted to be diagnosed with a developmental delay, compared with almost one-tenth among those born >2,500 g and 39+ weeks. A BW threshold of <1,250 g would identify children with the highest risk of delay; GA as an additional criterion would prevent overlooking high-risk children born <30 weeks but at higher birthweights. Physicians should monitor children with high-risk birth characteristics and refer them, if appropriate, for formal evaluation. EI programs may use these findings to guide determination of automatic eligibility criteria.