Background More than one in 10 of all prisoners in England and Wales are Foreign Nationals. This article discusses whether the research applications to one London prison are aimed at understanding a prisoner population characterised by significant multinational and multilingual complexity.

Methods We studied all accessible documents relating to research undertaken at a women's prison between 2005 and 2009 to assess the involvement of Foreign National prisoners and women with limited English. The source of information was prison research applications and protocols. We also looked at available final research reports and journal articles.

Results Two key findings emerged from this study. First, studies at this prison frequently excluded Foreign National prisoners and women with limited English. Second, Foreign National prisoners were often clustered as a homogeneous category in the research reports reviewed. This is despite their diverse cultural backgrounds, their variable immigration status and their differing competence in English, all of which affect their lives.

Conclusions The failure to include and/or identify social subgroups of the population can undermine the value of research, including, in the case of the study prison, funded health research. This can compromise associated needs assessments and service delivery, particularly important in already disadvantaged populations; this may encourage and/or perpetuate a range of health inequalities. There is a pressing need to examine cultural exclusion in other health and criminal justice settings, to assess the ways in which—and the extent to which—such exclusion may compromise the merit of proposed and completed health and social research.