As American households become more diverse, they may actually grow larger. The average size of households with at least one foreign-born spouse was typically larger than those where both spouses were born in this country, according to the Census Bureau. In fact, the largest households belonged to the 4.8 million married couples in which both husband and wife were born outside the United States. But it seems men are to blame for the phenomenon. "The presence of a foreign-born husband is likely to coincide with large family size," says Dianne Schmidley, coauthor of "A Profile of the Foreign-Born Population in the U.S., 1997." The presence of foreign-born wives doesn't seem to be a determining factor on family size, she adds. Also, foreign-born husbands and their families are more likely to live with extended family members, thus pushing up the average household size.