Hi just been round my friends house to have a look at her lab, and noticed he only has one testicle with no other sac or visable signs of another one??
Is this a problem? will it drop later as he is only 10 months or should she investigate this more at the vets? This has never been pointed out to her at the vets or by anyone, and he doesn't seemed bothered about it!
Any advice please as I have never had a male with only one :)

It sounds like a retained testicle, cryptorchidism. The retained testicle hasnt dropped from the abdomen into the scrotum. This testicle will usually be sterile due to temperature within the body. This has been thought to be a heritable trait, most dogs have a castration to remove them. The abdominal testicle will be removed through the abdominal wall :)

Thanks Misswager, :) I am not sure if she was planning to have him neutered, so does she need to have it done due to the missing testicle? or is it safe just to leave him as he is?

It would be advisable to get the retained one removed if there's no sign on it by the time he's a year old, because the higher temperature in the abdomen means that over the years it's more likely to become cancerous. Whether or not she wants the normal one removed as well is up to her, but he should never be used at stud.

Thanks Jeangenie, I will let her know. :) he is a lovely pet dog and they dont wish to use him at stud. 

Well, some people prefer to get a dog with a retained testicle neutered. There are two reasons for neutering a dog with cryptorchidism. The first is to remove the genetic defect from the breed line. Since cryptorchidism is an inherited defect, dogs with this condition should not be bred.

Second, if the retained testicle is left in the body, the chances are increased that the dog will develop a testicular tumor (cancer) in the retained testicle. The risk of developing testicular neoplasia is estimated to be approximately ten times greater in dogs with cryptorchidism than in normal dogs. In fact, 53% of all Sertoli cell tumors and 36% of all seminomas occur in retained testicles. Additionally, 36% of all spermatic cord torsions are found in dogs with cryptorchidism.

I would personally get a castration done if it were my dog :)

is that left side

is that the dog left side my right or my left he dog right side look straight on at the dog.?

I had my boy in for surgery at 16 months, six months after we realised he was a womble :)

The vets argued for a full castration but I was not remotely convinced--he will never be allowed near a bitch in season, let alone be used at stud, and there are endorsements on his papers that I am more than happy to respect. I just didn't want his character or coat to change, but then this veterinary surgery believes in neutering animals at a stupidly early age. Happy to say I got my way, the retained testicle was removed and we promptly parted company to find better vets!