BACKGROUND: Children of heroin-using women have a higher risk of unfavorable health and developmental outcomes. Although methadone maintenance treatment (MMT) has been widely used to treat heroin-using pregnant women, potential effects on accessibility and utilization of healthcare service for their offspring are less explored. METHODS: We used four national registry and health insurance datasets in Taiwan from 2004 to 2009 to form a population-based matched retrospective cohort study. A total of 1056 neonates born to women in the MMT program (857 born before mother's enrollment in the MMT program [BM], 199 born after mother's enrollment in the MMT program [AM]) was established; 10547 matched non-drug [ND] exposed neonates were identified for comparison. Outcome variables included offspring's health insurance coverage and utilization of preventive, outpatient, and emergency room cares in the first year after birth. RESULTS: Infants born to mothers on MMT were more likely to have no or incomplete insurance coverage (BM: adjusted odds ratio [aOR]=1.29, 95% CI: 1.10-1.53; AM: aOR=1.56, 95% CI: 1.14-2.13) as compared with the socioeconomic status-matched ND group. The BM infants appeared to have fewer preventive care visits (adjusted relative risk [aRR]=0.85, 95% CI: 0.80-0.90), whereas the AM infants utilized outpatient and emergency room services more frequently (outpatient: aRR=1.11, 95% CI: 1.01-1.23; emergency: aRR=1.46, 95% CI: 1.11-1.90). CONCLUSIONS: Addiction treatment and harm reduction programs for women of childbearing ages should be delivered in the coordinated framework that ensures comprehensiveness and continuity in healthcare and social services.