Based on this answer:

Use .dialog(widget) option to locate the div wrapper for the dialog. The wrapper contains all the markup used for the dialog including header, title bar and close button; and the dialog content itself. Here is one way to invoke the method and hide the title bar:

$(#id).dialog({

    autoOpen: false

}).dialog(widget).find(.ui-dialog-title).hide();​

You can then use CSS to eliminate unnecessary margin, border and padding. For example:

.ui-dialog-titlebar {

    float: right;

    border: 0;

    padding: 0;

}

.ui-dialog-titlebar-close {

    top: 0;

    right: 0;

    margin: 0;

    z-index: 999;

}

Here is a demo based on above code plus it adds the necessary styles using jQuery.