Private-equity firms have been flocking to behavioral health deals in recent years. The lower exit activity stems partly from the fact that the behavioral health industry overall is still early in its investment life cycle—meaning a lot of firms recently made investments that they likely will exit in the coming years, said Kara Murphy, a partner with Bain & Company.

Ms. Murphy said inpatient psychiatric treatment—where Acadia competes with other businesses—is one of the more mature sub-sectors compared with other areas of behavioral health, such as autism. She said those behavioral health businesses changing hands have done so at high-multiples.