Using panel data from Rural Peru we explore the role of institutional thickness on furthering the effects of key infrastructure investments on pro-poor growth. Institutional thickness is characterised here as the result of a combination of four interrelated characteristics: (a) the presence of organisations signalling collective action; (b) the degree of productive asset inequality; (c) the degree of inequality of opportunities and (d) the degree of political fragmentation. The paper shows that institutionally thick environments do contribute to amplify the effects of public infrastructure on income growth for those belonging to the poorest tercile, allowing poverty to be more responsive to growth. © 2011 John Wiley & Sons, Ltd.