Drawing upon innovative research methods this article provides the first Irish estimates of opiate use based entirely on non-medical data. These estimates are based on the report Baseline Findings from the ROSIE Study by Comiskey and Cox (2005), commissioned in 2002 by the Irish Government's National Advisory Committee on Drugs (NACD). In order to place these estimates in context we first provide a background to the probation and welfare service in Ireland; we then provide a picture of known opiate use to date; and finally we introduce the methods we used to provide new results on the prevalence of opiate users in Ireland.