<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by monahos:
The RER B runs through the rough northern suburbs of Paris. As a streetwise French-speaking male I still do not feel especially comfortable on those trains late at night. The express trains do not stop between the last city station and the airport, and are therefore less likely to carry troublemakers.
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Even during the daylight hours, gangs of thieves operating from stops between Gare du Nord and CDG have been stealing luggage and other items from tired passengers on crowded trains. If you use the RER, do as Monahos says and take the trains that bypass most of the stations on this route north of Gare du Nord.
At night, it's even spookier. Tourists headed towards the airport at night loaded with bags from a day of shopping are prime targets. Also, when returning make sure you take the RER B3 headed for CDG and not the B5 that goes to Mitry-Claye. When I stay at this hotel on one day trips, if I am unable to return to CDG by 8:00 p.m., I'll take the taxi. It's safer.