[kobezzza]

window.onload = function () {
	document.getElementById("country").onchange = function () {
		var
			group = document.getElementById("region").childNodes,
			$val = this.value, i, name;
		
		for (i = group.length; i--;) {
			if (group[i].nodeType !== 1) { continue; }
			
			name = group[i].getAttribute("name");
			
			if (name === $val || $val === "-1") {
				group[i].style.display = "";
			} else { group[i].style.display = "none"; }
		}
	};
};

<select size="1" name="country" id="country">
	<option value="-1" selected="">Выберите страну</option>
	<option value="0">Другая</option>
	<option value="1">Россия</option>
	<option value="2">Литва</option>
</select>

<select size="1" name="region" id="region">
	<option value="-1" selected="">Выберите регион</option>
	<option value="0">Другой</option>
	<option name="1" value="1">Калининград</option>
	<option name="2" value="3">Сувалкия</option>
	<option name="2" value="4">Жемайтия</option>
	<option name="1" value="5">Нижегородская </option>
	<option name="1" value="6">Воронежская</option>
</select>