I'd say it's Mexican-Americans who smoke far less than Mexicans in Mexico. I forget where I saw the stat, but Mexico has a higher percentage of smokers than the US does. I just chalked up the difference between Mexicans in Mexico and Mexicans and Mexican-Americans in the US to personal finances. Cigarettes have gotten increasingly expensive in the US, and represent an exorbitantly priced luxury to lower-wage earners trying to make a living here. When immigrants feel the need to be frugal in order to gain a foothold in the US, there's no room for that kind of thing, and by the time they've gotten established with homes, kids in school, and the like, they've lost the habit and their kids for the most part haven't picked it up.