This paper describes the process evaluation of an out-patient detoxification service (ODS) established by Drug Health Services (DHS) to increase the supervised withdrawal options for substance users in a Sydney metropolitan Area Health Service. The ODS aimed to provide a safe and effective supervised withdrawal to substance users who were at low risk of severe withdrawal, engage those with severe dependence in further treatment and increase the involvement of general practitioners (GPs) in the medical care of ODS clients. During its first 10 months of operation, the ODS received 199 inquiries, assessed 82 individuals and admitted 76 clients for detoxification. Withdrawal treatment proceeded without complications and within the expected time frames. Fifty-four clients completed withdrawal, 10 ceased treatment, 10 remained in treatment without completing withdrawal and two were transferred elsewhere. Clients who injected substances (mainly heroin) daily at admission, compared to others, were less likely to complete withdrawal and more likely to use a range of non-prescribed substances during withdrawal. One-fifth of clients went on to further treatment with DHS, attending at least once. Overall, the ODS met its goals, providing a safe and effective supervised withdrawal to local residents, especially women, young people and those withdrawing from benzodiazepines who had significant substance dependence, impairment and previous alcohol and other drug (AOD) treatment. Non-injecting substance users benefited most from the ODS in terms of withdrawal completion and ongoing treatment. The level of GP involvement in the conjoint care of ODS clients remained constant over time. The development and expansion of the ODS are discussed.