Recently, it has not been rare for psychiatrists to treatment disorders and provide consultation on mental health problems for people from different cultures. The following is a brief outline of mental disorders and mental health problems of the people who immigrated in culturally different societies. In reviewing the literature, most of the reports demonstrate that the admission rate for schizophrenia is higher among immigrants than among people remaining in their original countries or among native-born people of the host countries. Furthermore the prevalence of mood disorders in community surveys is reported to be higher among immigrants than among native-born people of the host countries. In regard to gender difference of vulnerability to cross-cultural immigration, the prevalence rate for mental disorders is reported to be higher in female immigrants than male immigrants. Psychological adaptation of Japanese war orphans returned from Mainland China four decades after WWII revealed that psychological problems became exacerbated three months after resettlement in Japan and took three years to recover. Three major psychological symptoms that manifested in resettlement were obsession, somatization and depression. It is hypothesized that the acculturation process can be divided into four layers: the behavioral level, intellectual level, representative level and emotional level. The study of the acculturation process of Japanese war orphans demonstrated that it gradually proceeded from a surface level to deeper levels, namely from the behavioral level-->intellectual level-->representative level-->emotional level. The relationship of psychological adaptation and acculturation process is reported to be complicated. The acculturation process does not necessarily accompany psychological adaptation and vice versa. Impact of immigration on psychological manifestation revealed the following vicissitude: the asymptomatic phase for two months after resettlement-->hypochondriacal phase-->depressive phase-->paranoid phase. The vicissitude of psychological manifestations of the impact of immigration may be a reflection of the four layers of adaptive mechanisms (G. Vaillant).