anyone?

Presumably, you mean the Page_Load method...?

OK.

If that is how your users are referenced in your database... You could also
use a stored procedure...

protected void Page_Load(object sender, EventArgs e)
{
   strConnectionString = "<connection string>";
   strSQL = "SELECT * FROM MyUsers WHERE UserID = '" + User.Identity.Name +
"'";

   using (SqlConnection objSqlConnection = new
SqlConnection(mstrConnectionString))
   {
       objSqlConnection.Open();
       using (SqlCommand objSqlCommand = new SqlCommand(pstrSQL,
objSqlConnection))
       {
           using (SqlDataAdapter objDA = new SqlDataAdapter(objSqlCommand))
           {
               using (DataSet objDataSet = new DataSet())
               {
                   objDA.Fill(objDataSet);
                   if (objDataSet.Tables[0].Rows.Count > 0)
                   {
                       // get any additional user details...
                       Session["UserExists"] = true;
                   }
               }
           }
       }
   }
}

The above is merely one of several methods you could use, and is not
particularly robust, but it should get you started...