As our knowledge about addiction is increasing the association between mental illness and addiction is better understood. The controversy about the appropriateness of the term Dual Diagnosis to describe such a heterogeneous group of patients has sparked a debate on treatment and assessment models. It highlighted the fact that as far as treatment modalities are concerned, one size might just not fit all. Dr Mouton reviews current knowledge on co-morbidity in the addiction field. Focusing on more than psychiatric co-morbidity, he also looks at physical, social, psychological, spiritual and cultural components affected by addiction. Describing the role of the psychiatrist in addiction care he poses the questions: What if dual diagnosis is actually the key to better understanding of our patients? What if this knowledge leads to more individualised treatments? And are we ready for personalised treatment in the addiction field?