We used the nationwide Swedish Family-Cancer Database to analyse cancer risks in 613,000 adult immigrants to Sweden. All the immigrants had become parents in Sweden and their median age at immigration was 24 years for men and 22 years for women. We calculated standardized incidence ratios (SIRs) and 95% confidence intervals (CIs) for 18 cancer sites using native Swedes as a reference. Data were also available from compatriot marriages. All cancer was decreased by 5% and 8% for immigrant men and women, respectively. However, most of the male increase was due to lung cancer for which male immigrants showed a 41% excess. Among individual cancer sites and immigrant countries, 110 comparisons were significant, 62 showing protection and 48 an increased risk. Most of the differences between the rates in immigrants and Swedes could be ascribed to the variation of cancer incidence in the indigenous populations. Some high immigrant SIRs were 5.05 (n = 6, 95% CI 1.82-11.06) for stomach cancer in Rumanian women and 2.41 (41, 1.73-3.27) for lung cancer in Dutch men. At some sites, such as testis, prostate, skin (melanoma), kidney, cervix and nervous system, the SIRs for immigrants were decreased; in some groups of immigrants SIRs were about 0.20. The highest rates for testicular cancer were noted for Danes and Chileans. Women from Yugoslavia and Turkey had an excess of thyroid tumours. All immigrant groups showed breast, endometrial and ovarian cancers at or below the Swedish level but the differences were no more than 2-fold.