Evidence suggests that demand-side barriers may be as important as supply factors in deterring patients from obtaining treatment. Yet relatively little attention is given, either by policy makers or researchers, to ways of minimizing their effect. These barriers are likely to be more important for the poor and other vulnerable groups, where the costs of access, lack of information and cultural barriers impede them from benefiting from public spending. Demand barriers present in low- and middle-income countries and evidence on the effectiveness of interventions to overcome these obstacles are reviewed. Demand barriers are also shown to be important in richer countries, particularly among vulnerable groups. This suggests that while barriers are plentiful, there is a dearth of evidence on ways to reduce them. Where evidence does exist, the data and methodology for evaluating effectiveness and cost-effectiveness is insufficient. An increased focus on obtaining robust evidence on effective interventions could yield high returns. The likely nature of the interventions means that pragmatic policy routes that go beyond the traditional boundaries of the public health sector are required for implementing the findings.