I totally agree to take him to the vet. But on another note my chihuahua had a similar issue he was loosing hair on his back left hind leg. In my case it ended up being the food I had him on. So I switched him to an all natural one and within weeks all his hair was back. I'll give you the link just incase your curious. Hope it turns out to be something simple like that and nothing too serious. Keep us posted and in the meantime I will keep you and your little one in my thoughts.http://http://healthypetnet.com/Heal...aspx?realname=