A list of outpatient clinics was developed in 1997–98 as an outcome of the Developmental Ambulatory Classification Study conducted by the National Hospital Cost Data Collection (NHCDC).

During 2011, the list was updated to accommodate the increase in services that were previously provided to inpatients being undertaken as outpatient services. This also included a full review of the classification in response to the National Health Reform Agreement 2011, which provided for the introduction of a national activity based funding (ABF) system. The aim was to develop a classification system for use with non-admitted services for ABF purposes.

The classification has been reviewed regularly from 2012–19 to ensure the classification's relevance and ability to meet the needs of the users.

In April 2020, the list was updated to include codes supporting services related to coronavirus disease (COVID-19).

Tier 2 classes provide a consistent framework for counting non-admitted service events. They are based on an assessment of both the type and specialty of the health-care professional providing the service and the nature of the service provided. This has resulted in a number of classes that is sufficient to ensure clinical meaningfulness and exclusivity across the spectrum of non-admitted services.

The classes are also grouped into a number of categories that reflects the type of service provided and the health-care professionals that typically provide the service. The classes are grouped into four categories, as follows:

• procedures
• medical consultation
• stand-alone diagnostic
• allied health/clinical nurse specialist intervention.