This study analysed the association between country of birth and psychotic, affective, and neurotic disorders in seven immigrant categories, after adjustment for demographic and socioeconomic factors. A 2-year national cohort study of 4.5 million individuals in the age group 25–64 years was performed. Swedish national registers including individual demographic and socioeconomic data were linked to the hospital discharge register. Cox regression was used in the analysis. Several groups of immigrants, both men and women, had risks of hospital admission for psychotic, affective, or neurotic disorders compared to the Swedish-born reference group. The impact of demographic and socioeconomic factors on these risks seemed to be larger for men than for women. For foreign-born men, several of the risks no longer remained significant after adjustment for income and marital status. In contrast, most of the risks for foreign-born women remained significant after adjustment for income and marital status. Low income and being single were associated with an increased risk of psychiatric hospital admission. These results represent important knowledge for clinicians and public health planners who are involved in treatment and prevention of mental disorders among certain groups of immigrants, and among low income men and women irrespective of immigrant status.