Case studies of immigrant groups ave contributed significantly to theo
retical developments in the fields of immigration and ethnic studies.
The focus on the immigrant group as a whole has resulted in ignoring i
mmigrant subgroups, reducing ethnicity to national-origin. Ethnically
diverse immigrant groups contain more than one type of ethnicity. Inte
rnal ethnicity refers to the presence of ethnic groups within an immig
rant group. It is argued that, in? the destination country, the immigr
ant subgroups who were already minorities in the country of origin are
less assimilated than the immigrant subgroup which runs part of the m
ajority population. Survey data collected in a probability sample of I
ranians iii Los Angeles allow lis to address this issue. Ethnicity of
the Muslim majority in the United States is compared with that of Arme
nian, Bahai, and Jewish ethno-religious minorities from Iran. The data
analysis supports the argument, and further shows that pre-migration
ethnicity is an important and neglected aspect of post-migration ethni
city.