Lost serial number?

You should be able to locate the serial number on the hardware: http://support.apple.com/kb/HT1349

What stuff requires the serial number for your computer? I don't recall ever needing to use that number for anything and I've been using Macs since 1984. I'm not saying it's never needed for anything, just that it's not something you should need frequently. Are you confusing this number with the serial numbers for all your different purchased applications?

I've been asked for my serial number with support requests and such. Other than that, I don't know anything that uses it.

About this Mac->More info->Hardware->Serial Number

I was looking into this a little, and it looks like you might be able to get the serial number back in the about window by resetting the PRAM ( http://docs.info.apple.com/article.html?path=Mac/10.6/en/26871.html ), though this is an old article and they claim that the issue was fixed, as far as PRAM. Still, you can give it a try.

It also looks like having the main logic board replaced during a repair will prevent the serial number from being displayed. My understanding is that a chip on the logic board provides this information to the about box, so if the logic board is replaced it would no longer report the correct serial number, and therefor reports no serial number at all. ...as is my understanding 😉

So, was your logic board replaced during a repair?

...and there was one report of someone having a logic board replaced and then later seeing the serial number in the about box again, so.. hmmm... very mysterious.

Generally, if it doesn't appear in the About This Mac box, it won't show in System Profiler either.

My understanding is that a chip on the logic board provides this information to the about box, so if the logic board is replaced it would no longer report the correct serial number, and therefor reports no serial number at all. ...as is my understanding

That is correct.

there was one report of someone having a logic board replaced and then later seeing the serial number in the about box again, so.. hmmm... very mysterious.

Apple techs have access to a tool that can write the serial number into the new logic board. They don't always remember or take the time to do this.

Assuming that our responses allowed you to recover the serial number, thanks for the feedback. Good computing.

Only if you want service from Apple support. IIRC, you should be able to find it on the machine someplace.