What happens if you miss first leg of a connecting flight?

[tt]

Ok so I managed to get one of those cheap tickets to Brazil last month. The flight the there and back are connecting flights. On the return home, we are thinking of missing the first leg and catching the return flight on the second leg from the next city.  Is it possible to to do this or will they automatically cancel the rest of the trip since we didn't show up for the beginning of the return itinerary?

[yakrot]

Ok so I managed to get one of those cheap tickets to Brazil last month. The flight the there and back are connecting flights. On the return home, we are thinking of missing the first leg and catching the return flight on the second leg from the next city.  Is it possible to to do this or will they automatically cancel the rest of the trip since we didn't show up for the beginning of the return itinerary?

AFAIK as soon as you miss a leg the rest of your itinerary is cancelled

[TimT]

If its 1 itin they'll cancel the rest.

[Copernicus]

I missed the first leg on a return ticket once when flying Turkish Airlines (PRG-IST-PVG).  I had decided to take another route back to IST and after speaking with them on the phone, they suggested speaking with their sales office at the airport.  The sales rep at the airport was kind enough to let me use just the IST-PVG flight. 

Normally the itinerary is voided, but in my case I was lucky enough to be dealing with a really kind rep.  I guess you can always try.

EDIT:  I should add that my flight to IST was from a different country than Czech Republic and not even with Turkish Airlines.