The study of compulsivity has been of long-standing interest in psychiatry but has recently become a hot topic of research after being linked to over a dozen conditions. In their review, el-Guebaly and colleagues  present evidence that pathological gambling (PG) is a condition that shares more phenomenological, neurobiological, psychological and treatment-related commonalities with substance use disorders (SUDs) than with obsessive-compulsive disorder (OCD). The suggestion is that PG should be diagnostically re-classified as a `behavioural addiction? rather than an `impulse?control disorder? (ICD). The authors go on to argue that the compulsivity observed in PG is similar to that observed in SUDs and may represent a candidate endophenotype. The review presents a fresh and innovative approach to understanding these common and disabling disorders. We take this opportunity to present some of the potential challenges of adopting this approach for future research.