There is an increasing Middle Eastern diaspora, of which Iranian migrants are a major group. They are dispersed within the general population in the destination countries; this, together with the fact that many are political migrants, makes conducting population-based studies on this minority group challenging. UK policy mandates that we provide equal access to health and healthcare for them. The research evidence on which to base healthcare planning and provision decisions for the Iranian diaspora is, however, very limited. This study aimed systematically to review methods used in population-based health research on Iranians to learn lessons to apply to future planned epidemiological research. Nine databases were systematically searched and the references of relevant articles were scrutinised. Researchers known to have particular expertise of working with Iranians were contacted to help locate additional unpublished work and research in progress. Quantitative and qualitative studies on Iranians living abroad, but not in institutions, published in English or Persian, that reported recruitment strategy, sampling and data-gathering technique were eligible for inclusion. From 30 potentially eligible articles, 13 unique studies satisfied our inclusion criteria. There was considerable diversity in the questions posed, methodologies used and findings of these included articles. The topics included dental health, cardiovascular risk factors, sex roles, cultural identity and research methods. The study sample sizes ranged from 10 to 413 participants. Participation rate with snowball sampling ranged from 19% (postal questionnaires) to 99% (telephone interview); with convenience sampling from 33% to 57%; and using random sampling from 21% to 68%. Responders tended to be of higher socio-economic status than non-responders.Commonly, information on translation and cross-cultural validity of questionnaires was not reported. This is the first systematic review of methods in health studies of Iranians living abroad. We found only a few studies and considerable heterogeneity in the methods and findings of these included studies. Although there is a growing population of Iranians abroad and study of determinants of health in this ethnic minority group is vital, this review shows huge gaps in the evidence base.