In a cross-sectional study, we examined demographic factors and acculturation level with somatization among chronically mentally ill groups of immigrants (Russians and Latinos). Ninety Russian and 90 Latino patients attending a university affiliated Day Treatment Program were assessed on somatoform symptoms and acculturation by the 12-item somatization subscale of the SCL-90-R and by a 12- items short acculturation scale, respectively. Higher somatization was significantly associated to women, Russian ethnicity, high school or above level of education, shorter length of residence in the U.S., and lower acculturation. Interaction by ethnic group showed that somatization was influenced by the length of residence in the U.S. among Russians but not among Hispanics. In a multivariate model, higher somatization corresponds to female, Russian, and shorter residence in the U.S. (only among Russians). Length of stay in the host country rather than the level of acculturation influence the frequency of somatic complaints, modified by ethnicity.