Aim: Studies of drug use during pregnancy have generally focused on individual substances or specific combinations of drugs. The aim of this article is to increase our knowledge about polydrug use and pregnancy in a Nordic context by describing the sociodemographic characteristics of a clinical population of pregnant women with severe substance use, examining the scope and type of polydrug use and analysing factors associated with concurrent use of many, as opposed to a few, drugs. Method: A cross-sectional study of pregnant women on admission to compulsory care for substance abuse in Sweden between 2000 and 2009 (n = 119 women, representing 128 pregnancies). Data were retrieved from administrative registers and client records. Univariate links between demographic, social, obstetrical, treatment history variables and polydrug use were examined. Binary logistic regression was used to analyse the association between explanatory variables and polydrug use. Results: The average number of drugs being used concurrently was 2.65, and injection drug use was recorded in 73% of the pregnancies. Opiates and amphetamines were the most common primary drugs, followed by alcohol. The likelihood of polydrug use increased with first trimester pregnancy, planned (as opposed to emergency) committals, as well as the combination of partner substance abuse and injection drug use. Conclusions: Polydrug use was widespread among pregnant substance abusers. Policies, interventions and research often focus on individual drugs separately, but for clinical populations in particular there is a need to address drug use broadly, including a systematic recording of smoking habits. This also entails awarding more attention to those not eligible for established interventions, such as opiate maintenance treatment, and giving more consideration to a variety of life circumstances, such as partner drug use.