© 2015, BMJ. All rights reserved. Introduction: The effects of exposure to marijuana in utero on fetal development are not clear. Given that the recent legislation on cannabis in the US is likely to result in increased use, there is a need to assess the effects of prenatal cannabis exposure on fetal development and pregnancy outcomes. The objective of this review is to assess the effects of prenatal exposure to cannabis on pregnancy outcomes (including maternal and child outcomes). Methods and analyses: Major databases will be searched from inception to the latest issue, with the aim of identifying studies that reported the effects of prenatal exposure to cannabis on fetal development and pregnancy outcomes. Two investigators will independently review all titles and abstracts to identify potential articles. Discrepancies will be resolved by repeated review, discussion and consensus. Study quality assessment will be undertaken, using standard protocols. To qualify for inclusion, studies must report at least one maternal or neonatal outcome post partum. Cross-sectional, case-control, cohort and randomised controlled trials published in English will be included. In order to rule out the effects of other drugs that may affect fetal development and pregnancy outcomes, studies will only be included if they report outcomes of prenatal exposure to cannabis while excluding other illicit substances. Data from eligible studies will be extracted, and data analysis will include a systematic review and critical appraisal of evidence, and meta-analysis if data permit. Meta-analysis will be conducted if three or more studies report comparable statistics on the same outcome. Ethics and dissemination: The review which will result from this protocol has not already been conducted. Preparation of the review will follow the procedures stated in this protocol, and will adhere to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Ethical approval of data will not be required since the review will use data that are already available in the public domain through published articles and other reports.