We investigate whether regional social capital is associated with a company’s discretionary disclosures of non-GAAP earnings. The US county level social capital is used to capture the informal supervisory instrument of regional social capital. The two dimensions of social capital, dense networks and strong norms in regions with high social capital, cause reciprocity, integrity, and organizational citizenship. Using a panel of US companies, we find that companies located in regions with high social capital (1) are more likely to disclose non-GAAP earnings, and (2) their non-GAAP earnings disclosures have higher quality. These findings are robust to controlling for demographic features, substitute proxies for regional social capital, and using two-stage least squares and propensity score matching approaches. Furthermore, we implement a mediator analysis and show that companies in high social capital regions have lower costs of equity capital because they are more likely to disclose non-GAAP earnings, and their disclosures are of higher quality. Overall, the findings indicate that the informal institutional factor of regional social capital is associated with the crucial voluntary disclosure tool of managers’ non-GAAP earnings.