BACKGROUND: Substance use in pregnancy is potentially harmful to both the fetus and pregnant woman. At the Royal Women's Hospital, the Women's Alcohol and Drug Service (WADS) provides pregnancy care and counseling for women who have complex drug and/or alcohol issues and psychosocial needs. Women who are stable on pharmacotherapy attend the general pregnancy clinics. RESEARCH QUESTION: What are the maternal characteristics, pregnancy and neonatal outcomes for a group of women attending for pregnancy care who were on pharmacotherapy substitution treatment, being prescribed buprenorphine or methadone? PARTICIPANTS AND METHODS: All women prescribed buprenorphine or methadone from September 2005 to December 2006 were identified by the hospital pharmacy department where prescribing permits are retained during the woman's pregnancy and postnatal period. Data were collected from medical records and a specific Drug and Alcohol Service database and analysed using descriptive statistics. RESULTS: Ninety-eight women were identified; 78 were prescribed methadone and 20 buprenorphine. Of these, 76 women also used other substances: tobacco (63%); cannabis (39%); and heroin (37%). Women who received no antenatal care had poorer outcomes overall. Twenty-four percent of live-born infants ≥33 weeks gestation (22/91) required medication for withdrawal. There was no difference in medication requirement where mothers were polysubstance users (18/70; 26%) compared with those who were not (2/21; 19%) (p=0.78), although these small numbers should be viewed with caution. The mean time until medication was required was 3.47 days. DISCUSSION: A significant proportion of infants whose mothers used buprenorphine or methadone in pregnancy displayed enough symptoms of withdrawal to require medication. This is therefore an important clinical issue of which care providers need to be aware. CONCLUSION: Further prospective research is required to explore whether factors such as specific substances are more likely to be associated with infant withdrawal.