This paper, rooted in agency theory, explores the intricate relationship between stock price crash risk and customer concentration within the context of Iran, a developing nation. Uti- lising innovative indicators to measure corporate and government customers, we address inconsistent findings in existing research and offer fresh insights into stock price crash risk dynamics. Focusing on 82 companies listed on the Tehran Stock Exchange from 2013 to 2020, our study employs a robust methodological framework, including panel data, multiple regression and three distinct metrics to measure customer concentration. Specifically, we introduce the proportion of significant customer sales, the Herfindahl-Hirschman Index, and a Ranking Index based on substantial customer sales. Our investigation reveals a noteworthy inverse relationship between the highest concentration level of corporate customer con- centration, as measured by the Ranking Index, and stock price crash risk. Similarly, we establish an inverse association between the Ranking Index for government customer con- centration and stock price crash risk. Moreover, institutional investors positively influence the correlation between corporate customer concentration and stock price crash risk but do not exert a discernible impact on the relationship between government

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