My USB mouse only scrolls in one direction (up)

Assuming you are talking about the USB mouse that came with your Mac, get a clean piece of paper and put it on the desk. Turn your mouse upside and put the rubber scroller ball on the paper. With moderate pressure, roll the mouse around on the paper for about 30 seconds. Now try using the mouse. Repeat as needed.

Did you ever think to clean your mouse? Balls tend to clog with crap after some time and the optics may also need cleaning.

swb gives good advice. If that didn't work:

How to really clean your Mighty Mouse (with caution!):

http://support.apple.com/kb/HT3226?viewlocale=en_US

and:

http://web.mac.com/karelgil/iWeb/MacWebSite/MightyMEng.html

http://www.linklink.co.uk/apple-computers/cleaning-inside-and-dismantling-the-ap ple-mighty-mouse/

Absolutely excellent advice. Worked perfectly. thank you

Thank You!!!

After 3 weeks of fumbling with it and banging on it and having to use scroll bar...fixed 🙂

I really didn't think this would work but it did! Thank you so much!!

Same problem here with scrolling, I can't believe it but the FIX WORKED! Wahoo!!!!

1000 Thanks !!!

thank you... mouse scrolling in one direction was driving me nuts- your solution sounded like the old days of smacking the top of a TV in the vain hope of improving the reception but it worked !

This worked for me! Thank you so much, that just revived and old mouse that I thought was broken.