Background: Most individuals in opioid maintenance treatment (OMT) have had serious polydrug problems in addition to opiate addiction. Prospective studies on substance use among pregnant women in OMT and their male partners on a national level have been scarce and therefore deserve attention.Methods: The European Addiction Severity Index was used to map substance use history among a Norwegian national cohort (2005–2006) of pregnant OMT women (n = 37) and their partners (n = 23), as well as substance use during the last month of pregnancy and 1 year later.Results: Lifetime substance use indicated an average of 8 years of heroin abuse before entering OMT. During the last month of pregnancy one woman and two partners reported using illegal substances, while 1 year later, one women and one partner reported having used illegal substances. The use of legal substances among the partners was significantly reduced from pregnancy to 1 year later (38–20%, p < 0.01), while the use of legal substances among the women increased from 8% to 19%.Conclusion: The results suggest that a majority of OMT mothers in Norway and their partners are able to abstain from most illegal substances 1 year after pregnancy, but the tendency of problem drinking among the women is a concern.