My 10 year old son's testes had to be removed due to thecancer, rhabdomyosarcoma, 5 years ago. now the doctor noticed that the other testes' size is larger than normal. what should i do?

Needs workup: He needs to have the other testis evaluated for cancerous growth. As you know this involves an ultrasound assessment and possibly an MRI and then surgery, if indicated. It's better to be safe than sorry.

I agree with good Dr: And given the history of your sons surgical diagnosis, it does need evaluation. But the other testicle will hypertrophy to some extent, even at his age. Hopefully that will expalin it! if is does, it will hypertrophy more during puberty. Good luck!

Further tests needed: Given the history i would also recommend further testing. Testes can increase in size at this age, so it could also be normal.

Imaging, exams, f/u.: One is always nervous about this but it would be relatively unusual to have it come back this late - although not impossible. As noted, u/s imaging, possibly and mri, and a good physical exam by a pediatric urologist with experience is key. Get him seen and followed closely. How his penile shaft and hair stage is may point to normal status too. A biopsy may ultimately be needed. Good luck.