At present, there are no reliable data to identify the number of patients who present for infertility investigations and who are current users of illicit drugs. Therefore, the full extent of this problem remains hidden. Estimates can be made on the basis of population use, although this lacks rigour. The use of illicit drugs can impact on infertility investigations, treatment, welfare of the child and parenting. Furthermore, it can result in serious legal sanctions, including imprisonment. There does not appear to be consistent practice across HFEA licenced clinics in either requiring: (i) the addicted patient to have a specified drug-free period before commencing investigations; or (ii) all patients to be routinely screened. As well as describing the extent of illicit drug use in the UK population, and therefore in those who present in clinic, this paper will discuss screening and encourages debate across clinics regarding a mandatory drug-free period and the development of an appropriate Standard Operating Procedure. [ABSTRACT FROM AUTHOR]