Traditional 'one-off' research studies are no longer considered sufficient to demonstrate the effectiveness of treatment programs. State-mandated clinical and administrative databases and treatment outcome monitoring systems (OMSs) are increasingly being recognized as necessary to provide current, representative, ongoing information that can immediately be fed back to service providers to improve the quality of services. OMSs can also provide reliable, aggregated and comparable data to inform the planning and development of treatment delivery services. Increasingly, routinely collected clinical data is being used to investigate alcohol and other drug (AOD) service delivery, client characteristics and to report on treatment outcomes. Debate persists as to whether OMSs should be mandated for use across jurisdictions or be locally-based and voluntarily undertaken, serving the needs of a smaller network of services. This article outlines the features, benefits and challenges associated with the design and implementation of OMSs in the AOD treatment sector. Particular reference is made to promoting and evaluating the impact of OMSs in Australia in an effort to enhance clinical service delivery and promote best practice in the AOD treatment sector.