well its not usual as you have already worked out...but there are also huge margins to "normal"...how old is he? lots of kids go through funny obsessions around 3 or 4 and often when they go to school and have more to think about and lots of kids to keep them busy it just stops....but even so i would have a chat with a paediatrcian because its certainly possible that its a behavior that he would be better without...and probably so would you!! good luck

Should I be worried? Any suggestions to stop it? Should I stop it?

Ever since he was able to walk, my son runs in circles and up and down. It reminds me of caged animals pacing, you would see at the Zoo. We live in a 1st floor flat so we dont have a garden. But we dont stay in all the time, his diet is good etc. I have asked him why he dose it and he says he is thinking, maybe it is for attention? I am a fairly active parent and engage him in activates, but I stop for one second to answer the phone etc.. Off he goes!
None of the other parents I know have seen any thing like this.

Any ideas?

well its not usual as you have already worked out...but there are also huge margins to "normal"...how old is he? lots of kids go through funny obsessions around 3 or 4 and often when they go to school and have more to think about and lots of kids to keep them busy it just stops....but even so i would have a chat with a paediatrcian because its certainly possible that its a behavior that he would be better without...and probably so would you!! good luck