There is now a considerable body of epidemiological evidence from developing countries and multilateral agencies that so called common mental disorders are common and disabling (e.g. Murray & Lopez, 1996; Patel et al. 1998). The logical next step is to identify efficacious and cost-effective health services interventions that can tackle the all-important ‘so-what’ question that is posed by doctors and policy makers in developing countries when confronted with startling prevalence statistics. The rise of evidence-based medicine has highlighted the need for quality trials that can inform and guide clinical practice. This editorial poses the question of whether we need treatment evidence from developing countries. The key issue is whether we can assume that psychiatric treatment evidence can be applied from one culture, or region, to another. If, for example, this was possible, then clinical practice in developing countries could be fairly well informed by trials conducted in the West. However, there are several factors that limit the cross-cultural applicability of treatment research in psychiatry.