The drug treatment outcomes research study (DTORS) assessed the outcomes, costs and benefits of drug treatment in England, this document presents a cost analysis of these services. The participants in this economic analysis were the adult treatment seekers who participated in baseline interviews for the DTORS and had an assessment for structured drug treatment. The analysis estimated the costs and benefits of structured drug treatment from baseline to the end of scheduled follow-up (one year), for all participants, including those who did not complete treatment. The average cost of drug treatment over the whole DTORS sample was estimated to be £6,064 from baseline to the end of scheduled follow-up. The use of health and social care services, accommodation and the number of participants who had children in care was relatively low. The number of participants who reported committing offences decreased between baseline and follow-up. However, the estimated mean costs of offences were very variable and all had very high standard deviations.