Actually when exiting the RER you MUST have your ticket to get through the turnstile.

I did this transfer yesterday (February 21, 2005) from Pl. de Italie metro to CDG. Pl. de Italie is the metro station just past Goeblins. We left the Citadines Aparthotel Pl. de Italie at 7:15 AM. We took the metro to Opera and the 7:45 AM Roissybus to CDG. We were dropped off at terminal 2A for American Airlines at 8:10 AM. This was the first stop at the airport. We checked-in, cleared security, and were in the Admirals Club by 8:30 AM.

The Roissybus costs 8.30 Euros per person and departs from Rue Scribe (near the Opera metro and by the American Express office).

On Friday, February 18, 2005, we landed at CDG at 9:50 AM at terminal 2A on American Airlines. We did not check bags. We caught the Roissybus to Opera at terminal 2B (outside across from McDonalds; the signs say OPERA and OPERA is written on the sidewalk). Since we were the second pick-up, the trip into Paris took longer because we stopped at the other terminals. We were at Opera by 10:30. We took the metro from Opera to Pl. de Italie on line 7 (I think); no line changes were required. We checked into our aparthotel room a little after 11:00 AM.

JoeTro:

I recommend the Air France Bus which takes you to the Arc de Triomphe, and from there, do the Metro. BE INFORMED: the Air France bus NOW costs 12 EUROS, not 10 as is still advertised on many websites.

The convenience is that the exit from the international terminal to the /Air France bus-stop is right at baggage claim. It is true that you may have to walk up and down some stairs entering and exiting the Metro, but, all-in-all, this is a cheap, efficient method into Paris.
For return, I prefer not to be as frugal nor as flexible. I don't trust foul-ups: unplanned delays or detours causing you to be late to your hotel are one thing; similar delays in your departure, however, may cause you to miss your flight out. That can prove costly as well as inconvenient. So, I like to use a shuttle bus back to CDG- my favorite: airport connection (www.airport-connection.com) 25 Euros per person if you're willing to share your ride. It requires an advance 24-hour reservation, but can be done on-line and secured /paid by credit card. They pick up so that you arrive at the airport at least 2 hours before take-off. It works.

Air France bus to <b>Montparnasse</b>, then the metro line 6 to Place d'Italie, if you're going to do that...

Air France bus #4 to <b>Gare de Lyon</b>, then RATP Bus #91 to les Gobelins would save some back-tracking and stair-climbing (not to mention getting you closer to your destination).