In the US the Federal Aviation Administration mandates that every sport, or emergency, parachute system be inspected and re-certified as airworthy by an appropriately rated rigger every 120 days (in some other countries this is every 180 days).

Elsewhere on the site there is a breakdown of what your rigger will do during this process, but safe skydiving depends on the maintenance of a symbiotic relationship between the skydiver and their rigger.

For example, if you use a Cypres AAD, the battery has to be changed every 2 years or every 500 jumps (whichever comes sooner). Your rigger can tell when the battery was last changed, but they don't keep your log book! If you've been banging out the jumps, tell them so that they can install a new set and keep your rig airworthy.

If, during your previous maintenance checks, you've noticed anything that you think deserves a little extra attention or fixing, or if you have any concerns over the condition of your rig tell your rigger when you hand it over for it's inspection. If there is sewing to be done, a pouch or velcro to be replaced it's a lot easier to do it when the reserve is out of the container.

Main parachutes don't generally fall under the mandated maintenance category however, in the US the FAA mandates that every main parachute be repacked every 120 days, so if you've had a seasonal lay off, or haven't jumped for a few months, when you hand your rig over for inspection you should ask your rigger to inspect and repack the main for you as well.