OBJECTIVES: To determine the characteristics of dopamine D2 receptor gene (DRD2) polymorphisms in drug-exposed and unexposed neonates and the relationship to neonatal abstinence syndrome (NAS). DESIGN: Retrospective case-control analysis between drug-exposed and unexposed infants between DRD2 polymorphisms, drug exposure and NAS treatment. PATIENTS: Drug-exposed (n=48) and drug-free (n=49) infants born between March 1999 and December 2006. METHODS: Analysis of DNA for the Taq1A, -141Ins/Del and Ser311Cys DRD2 polymorphisms. Drug exposure was determined by antenatal maternal drug and alcohol history. Frequency measures of DRD2 polymorphisms were compared between drug-exposed infants, treatment NAS medication and with control infants. SETTING: Tertiary maternity hospital, Sydney, Australia. MAIN OUTCOME MEASURES: All infants were born in a good condition (25.7% <37 weeks gestation). Opiates (methadone and heroin) were used by 45 (93.8%) of drug-exposed mothers. The A2A2 allele was more common in drug-exposed infants (37 (77.0%) versus 23 (46.9%), p=0.003) but the A1A2 allele was more common in control infants (23 (46.9%) versus 4 (8.3%), p=0.00002). The-ins allele was more common in control (39 (79.6%) versus 20 (41.7%), p=<0.01) and unmedicated drug-exposed (14/25 (56%) versus 5/23 (21.7%), p=0.02) infants. The majority of infants (41 (83.7%) controls versus 41 (85.4%), p=1.000) expressed the least common, Ser polymorphism. CONCLUSIONS: DRD2 polymorphisms are detectable from DNA obtained from stored blood spots. The -ins allele is more common in control and unmedicated drug-exposed infants. Further study is recommended to explore postneonatal outcomes especially in relation to neuropsychiatric behaviours.