Following Eijffinger and Geraats (2006), we construct an index of transparency of banking supervisors that takes political, economic, procedural, policy and operational transparency into account. Based on a survey, we construct the index for 24 banking supervisors. There are large differences among transparency of supervisors. The average total score is 9.2 points (out of 15), whereas the minimum ... [Show full abstract] is 6.25 points and the maximum 12.75 points. The average of economic transparency is the highest, while the average score for policy transparency is the lowest. Our analysis suggests that it is very hard to identify factors that can explain these differences.