I have a question about travelling abroad after entering the US on an IR5 visa. My wife's parents just received their interview date set for October 4. After approval we will pay the USCIS immigrant fee right away. They will likely be entering the United States as soon as they receive their visas. My question is, it says it may take 90 days to receive the green card in the mail after paying the immigrant fee. We travel to Mexico over Christmas and New Years almost every year and we'd like to take them with us. Will they be able to re-enter the United States without that green card. Is the passport stamp good enough?