The purpose of this study is to identify the elements that can be implemented to achieve an ethical infrastructure, in small and medium enterprises. The ethical infrastructure is considered as a set of formal and informal systems, leadership, climate and culture, related to ethical issues. The research was carried out through interviews and focus groups with managers from 28 companies in Madrid, all signatories to the Global Compact. The identified key elements in SMEs are leadership, informal managerial and formal communication. (...) This study also explores different factors that influence the effectiveness, implementation, and sustainability of the ethical infrastructure in SMEs, discovering some factors that can act as both accelerators and barriers such as pressure from customers. Additional findings regarding the concepts of ethics and corporate social responsibility in SMEs, dilemmas and characteristics of the culture and climate are also presented. (shrink)