My iPhone 5S suddenly will not sync calendars with iTunes on my iMAC. I recently upgraded the iMAC to version 10.8.5. Am I missing a setting somewhere?

Hey Oynkus,

Thank you for visiting Apple Support Communities.

You state you updated your iMac to OS X 10.8.5. Did you update iTunes as well?

If so, you may find the calendar sync options under Info.

Sync contacts, calendars, and other info with iPod, iPhone, or iPad - iTunes Help

Sync contacts and other info with iPod touch, iPhone, or iPad

1. Connect your device to your computer.
2. Click the device button, then click Info.
   
3. Select the items you want to sync.
4. Click Apply.

Take care,

Nubz