ABSTRACT This study investigates the impact of bank concentration and financial development on economic volatility for the Organization of Islamic Cooperation (OIC) member countries. Employing dynamic panel models, we find no evidence that bank concentration is significantly related to economic volatility when it is entered independently in the models. Meanwhile, financial development lowers economic volatility. Extending the models to include market structure–financial development interaction, we note that the impact of bank concentration on volatility depends on the level of financial development within OIC countries. More specifically, the volatility-increasing effect of bank concentration tends to be moderated by financial development. Accordingly, in the wake of banking sector consolidation in these countries, policymakers and regulators in OIC countries should focus on further developing their financial markets such that the negative consequences of resulting market concentration can be mitigated.