Aim: To ascertain the design and operational characteristics of acute Medical Assessment Units (MAU) located within Australasian hospitals, and to compare these with formal standards promulgated by the Internal Medicine Society of Australia and New Zealand (IMSANZ). Method: Descriptive study based on responses to questionnaires mailed to clinical and nursing leads of MAU in March 2009 with follow-up reminders over 3months. Hospitals that had an MAU that met predefined criteria were identified from an IMSANZ directory of sites based on recent contact with IMSANZ members and health department personnel and interrogation of hospital websites and attendance lists at recent MAU workshops. Results: Questionnaires were returned from 32 of 50 hospitals (response rate 64%). Most MAU (15/22; 68%) were less than 2years old. MAU were smaller than recommended by IMSANZ. Sixty-eight per cent were located over a 5-min walk from the emergency department (ED). Delay in transfer of patients from the ED to the MAU was common. The medical service to the majority of MAU was provided by General Medicine physicians and cover was reduced at weekends. In the majority of MAU the emphasis on function was facilitating discharge of patients rather than managing patients with high acuity of illness. Conclusions: Our survey suggests that despite some variation in staffing and procedures, MAU seem to be well established and a promising means of decreasing ED access block. Future comparative study is required to evaluate further the effect of MAU on ED access block and ED length of stay.