unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ComCtrls, StdCtrls;

type
TForm1 = class(TForm)
TabControl1: TTabControl;
Button1: TButton;
procedure TabControl1DrawTab(Control: TCustomTabControl;
TabIndex: Integer; const Rect: TRect; Active: Boolean);
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var tb:array of TButton;
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.TabControl1DrawTab(Control: TCustomTabControl;
TabIndex: Integer; const Rect: TRect; Active: Boolean);
begin

if high(tb)<TabIndex then setlength(tb,TabIndex+1);
if tb[TabIndex]=nil then begin
tb[TabIndex]:=TButton.Create(TabControl1);
tb[TabIndex].Parent:=TabControl1;
tb[TabIndex].Caption:='X';
tb[TabIndex].Left:=rect.Left;
tb[TabIndex].Top:=rect.Top;
tb[TabIndex].Width:=20;
tb[TabIndex].Height:=rect.Bottom;
tb[TabIndex].Visible:=true;
end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
TabControl1.Tabs.Add('qwerty');
end;

end.