Thank you for the answer, and sorry for didn´t show you my complete code.I have to use the code below, to know wich checkbox is selected.With your solution, I will resolve the problem with the command c.length.But I still have a problem with the command "c.checked", when I have just one checkboxvar c = document.AlterarExcluirForm.checkbox;for ( var i=0; i < c.length; i++ ){if ( c.checked == true ){tem_selecao = true;break;}}