Cost research has become an important perspective in recent years, both in the general health as well as the substance use area. In the field of illegal drugs, an exemplary overview will be provided on the status and contribution of cost research on the topic of illicit opiate addiction and its treatment. From a research tradition spanning almost thirty years emerges the consistent and clear knowledge that the lion share of social costs associated with illicit opiate use relates to criminality or the various levels of criminal justice. In the field of treatment it is consistently shown that the predominant modes of treatment - primarily substitution therapy - produce positive cost-benefit ratios. The most difficult challenge, however, seems to be the interpretation and application of these seemingly clear states of knowledge and their determinants to the practices of opiate policy and treatment. The documentation of the cost dynamics for illicit opiate addiction and its treatment up to this point battles with the issues that: a) they take effect in a socially constructed environment of illegality; b) they emerge on the basis of specific and narrow research perspectives and thus are not generalizable to naturally given populations; and c) in their current form contribute little to the building of an optimised intervention system.