<div class="divpere" >
<div class="divfille1" ><label>CIVILITE:</label></div>
<div class="divfille2" >
<input name="samename" type="radio" id="mademoiselle" runat="server" /><label for="mademoiselle"> Mademoiselle</label>
<input name="samename" type="radio" id="madame" runat="server"/><label for="madame">Madame</label>
<input name="samename" type="radio" id="monsieur" runat="server"/><label for="monsieur">Monsieur</label>
</div>
</div>
You should mention the name attribute
for your radio buttons and Don't forget to mention the same name values for all three radio buttons...