I'd say that it really depends on your shoe size.

you start to see Adidas or Nike shops around.
There is one Dien Bien Phu. And i think one also in Vincom Tower.

As to know if their genuine brand, it's another story and/or thread to start or continue here.

with my show size (10 1/2 - 11 or 43-44), i stopped looking as i simply never find shoes beside a left over from a 10 year old stock in the back of a doggy shop.
I usually wait for a trip back home or a nice long week-end in Thailand.

Though you might be able to find some in Saigon if you ever go there, as their shopping is more developed.

Good luck! (and i mean it, seriously)

There's a new adidas shop on Hang Gai.
You can find (EU) 43, 44 size in adidas, Nike, Puma shops. I have a pair of adidas shoes size 43. I bought them in adidas shop on Pho Hue.
You can find some 45 in Boo or Shark shops but the quality is...

Thanks folks. Shoe size isn't a problem. I see shoes for sale in the shops around North end of Hoan Kiem and I'm wondering if anyone has bought a good pair of running shoes there.

I think you mentioned about Hang Dau (Hàng Dầu). They sell fake shoes from China, some are old and were bought in much cheaper price.
Good? I don't think so but they're really cheap if you can barter.
With lot of luck, you may find some genuine shoes there but they're second-handed.

Adidas shop on Hang Gai str is my choice! They have very good shoes there.

cheers,

For readers with larger feet...

there is an adidas shop in vincom that has a few options at 12us-46eur..

Thanks for the suggestions. I finally bought a pair at the Adidas store in the mall on the south end of Hoan Kiem lake (can't remember what it's called). There were several shops there that seemed to have a decent selection.