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>