How to hide dynamically added div from code behind

The other solutions are correct in setting runat=server and then hide the div from the server. But the div you intend to hide can contain elements which may be referenced somewhere in your script and your javascript will throw null reference error if they are not there on the page.

To avoid that use the following code:

yourDiv.Style.Add(HtmlTextWriterStyle.Display, "none");

This sets Display css property to none to hide the div instead of not adding the element entirely.

This approach is much cleaner and safe then just setting visibility to false.

I believe the base class for all ASP.NET WebForms controls is HtmlControl which has a Visible property.

sample-div.visible = false;