This paper investigates the relationship between stock price crash risk and customer concentration in Iran, a developing nation. Using three novel indicators to measure corporate and government customer concentration (proportion of significant customer sales, Herfindahl-Hirschman Index, and a Ranking Index), the study examines data from 82 companies listed on the Tehran Stock Exchange from 2013 to 2020. Results show an inverse relationship between the highest concentration level of corporate and government customer concentration (measured by the Ranking Index) and stock price crash risk. Institutional investors positively moderate the relationship between corporate customer concentration and crash risk but not the relationship between government customer concentration and crash risk.
