Although relatively rare in industrialised and developed countries, the phenomenon of young people spending much of their time in urban environments in the context of extreme poverty is common in the cities of the developing world. Interventions are generally focused on bringing the children into education systems. However, the children have often been exposed to a range of factors likely to impair cognitive development, such as trauma and substance abuse, potentially limiting the efficacy of education programmes. A systematic review was performed of studies reporting cognitive function data of street children in developing countries. Only seven studies were found, which reported on 215 individuals. A review of the studies revealed a pattern of below normal general intellectual function and neuropsychological impairments. In those studies where measures of general intellectual functioning were reported, e.g. IQ, comparisons of effect sizes were made. This revealed that cognitive impairment appeared to be relatively minor in samples from Indonesia and South Africa but somewhat larger in samples from Ethiopia and Colombia. The results suggest cross-cultural variation in the effects of street living on cognitive development. However, in general, there is a pattern of lower than normal cognitive performance which is comparable to that observed in studies of homeless children in the USA