Aims: This study investigates the risk of small for gestational age (SGA) in relation to country of origin of the mother. The role of psychosocial resources, socioeconomic and lifestyle factors was examined in different causal models. Methods: Among all pregnant nulliparous women in the city of Malmö, Sweden, who gave birth in 1991 - 92, 872 (87.7%) women completed a questionnaire during their first antenatal visit. The study was carried out among women whose pregnancies resulted in a singleton live birth (n=826); 22% (n=182) of these women were foreign-born. Results: Fifty-five (6.7%) of the infants were classified as SGA, 37 (5.7%) of mothers of Swedish origin and 18 (9.7%) of foreign origin. SGA deliveries were much more prevalent among Middle East- and North Africa-born women (22%) and sub-Saharan-born women (15%). In all, women of foreign origin had increased odds for delivering SGA babies (OR=1.8, 95% CI=1.0,3.2). In a multivariate analysis psychosocial and socioeconomic factors explained 30% and 40%, respectively, of the increased SGA risk. Psychosocial factors seemed to be more prominent risk factors for SGA among mothers of foreign origin. A possible synergistic relation was demonstrated between foreign origin of the mother and low social anchorage. Conclusions: This study showed that psychosocial factors, most probably linked to a disadvantaged social situation, could be the theoretically most important focus for preventing SGA in immigrant women. This could also further support a hypothesis of a link between psychosocial stress and SGA in general. However, this should not exclude the need for intervention in the antenatal care system in terms of specially tailored support and education.