This paper considers how a manager decides to disclose or withhold segment information in a capital market setting. In particular, we develop a multi-period model in which a manager in each period decides how to allocate her effort between two businesses. The profit earned in each segment is determined by the manager’s effort and ability as well as each segment’s market profitability and inherent uncertainty. In this setting, in contrast to the expectation of segment disclosure being withheld due to conflicts of interest between managers and shareholders, we identify the conditions under which the manager rationally withholds segment information and achieves higher firm value. In a setting where the manager is concerned about the current stock price, disclosing more disaggregated information to the stock market does not necessarily lead to more efficient monitoring. The capital market values various segment earnings differently, and in response to this valuation, a rational manager may greatly alter her behavior, leading to inefficient outcomes.