Objective: To compare mortalities for selected groups of immigrants with the national average. Design: Analysis of mortality for adults aged 20-69 in 1970-2 and 1989-92 using population data from 1971 and 1991 censuses. Mortality of Scottish and Irish immigrants aged 25-74 was also compared with mortality in Scotland and Ireland for 1991. Setting: England and Wales. Main outcome measures: Standardised mortality ratios for deaths from all causes, ischaemic heart disease, cerebrovascular disease, lung cancer, and breast cancer. Results: In 1989-92 mortality from all causes was higher than the national average for Scottish immigrants, by 32% for men and 36% for women; for Irish immigrants it was higher by 39% for men and 20% for women; and for Caribbean born men it was lower by 23%. Ischaemic heart disease and lung cancer accounted for 30-40% of the excess mortality in Scottish and Irish immigrants. For south Asians, excess mortality from circulatory disease was balanced by lower mortality from cancer. Standardised mortality ratios for cerebrovascular disease in 1989-92 were highest for west African immigrants (271 for men and 181 for women). Conclusions: Widening differences in mortality ratios for migrants compared with the general population were not simply due to socioeconomic inequalities. The low mortality from all causes for Caribbean immigrants could largely be attributed to low mortality from ischaemic heart disease, which is unexplained. The excess mortality from cerebrovascular and hypertensive diseases in migrants from both west Africa and the Caribbean suggests that genetic factors underlie the susceptibility to hypertension in people of black African descent. Differences in mortality of immigrants in England and Wales widened between 1970 and 1992 and could not be explained by socioeconomic differences Mortality from all causes was higher than average for Scottish and Irish immigrants, and some of the excess could be accounted for by smoking habits, reflected by increased mortality ratios for lung cancer Mortality ratios for stroke and hypertension were highest in west African immigrants, indicating that better detection and treatment of hypertension is required in this group Mortality from all causes was low in Caribbean immigrants, largely due to low mortality from ischaemic heart disease Mortality from ischaemic heart disease remained high in south Asian immigrants and did not decline as fast as in the general population