Patients have been able to access clinical information from their paper-based health records for a number of years. With the advent of Electronic Medical Records (EMRs) access to this information can now be achieved online using a secure electronic patient portal. The purpose of this study was to investigate maternity patients' use and perceptions of a patient portal developed at the Mater Mothers' Hospital in Brisbane, Australia. A web-based patient portal, one of the first developed and deployed in Australia, was introduced on 26 June 2012. The portal was designed for maternity patients booked at Mater Mothers' Hospital, as an alternative to the paper-based Pregnancy Health Record. Through the portal, maternity patients are able to complete their hospital registration form online and obtain current health information about their pregnancy (via their EMR), as well as access a variety of support tools to use during their pregnancy such as tailored public health advice. A retrospective cross-sectional study design was employed. Usage statistics were extracted from the system for a one year period (1 July 2012 to 30 June 2013). Patients' perceptions of the portal were obtained using an online survey, accessible by maternity patients for two weeks in February 2013 (n=80). Descriptive statistics were employed to analyse the data. Between July 2012 and June 2013, 10,892 maternity patients were offered a patient portal account and access to their EMR. Of those 6,518 created one (60%; 6,518/10,892) and 3,104 went on to request access to their EMR (48%; 3,104/6,518). Of these, 1,751 had their access application granted by 30 June 2013. The majority of maternity patients submitted registration forms online via the patient portal (56.7%). Patients could view their EMR multiple times: there were 671 views of the EMR, 2,781 views of appointment schedules and 135 birth preferences submitted via the EMR. Eighty survey responses were received from EMR account holders, (response rate of 8.1%; 80/985). The majority of respondents indicated they would use the portal and access their EMR for future pregnancies (86.2%; 69/80). Approximately half looked at their EMR after a visit with their care provider (51.3%); 41/80) and 37.5% (30/80) viewed their EMR before, to prepare for their visit. The majority (65.8%) thought that the EMR improved their ability to understand and recall appointments and almost half (48.1%) thought that with the EMR they were less likely to repeat pregnancy information to caregivers. This study provides the first Australian evidence of a patient portal system, tied to an EMR, working effectively in a maternity care context. It provides new evidence that portals can deliver benefits to maternity patients in terms of providing quick and easy access to current personal and general health information and support patients in their ability to recall and prepare for appointments.