Several studies have reported poorer infant outcome among immigrants, but contrary evidence also exists. Between 1940 and 1999 more than a half million Finns emigrated to Sweden, which made Finns the largest minority group in Sweden. Our aim was to investigate fertility trends, parturients' background and pregnancy outcomes among Finns in Sweden, and to compare the findings with those obtained among Swedes in Sweden and Finns in Finland. The data came from the Finnish and Swedish Medical Birth Registers for the years 1987-1998. All deliveries by women born in Finland and having given birth in Sweden (N=33874) were compared with a 10% sample of all deliveries by Swedish parturients in Sweden (N=108549) and of all Finnish deliveries (n=75133). Among Finns in Sweden, the number of live births per 1000 women aged 15-49 years declined significantly in the late 1990s. The change in the total fertility rate was less dramatic: the rate for Finns in Sweden followed the total Swedish rate although it remained from 5% to 10% higher up to the mid-1990s. Finns who had given birth in Sweden were older, had a higher parity and a higher prevalence of previous miscarriages, and smoked more often than did Swedes in Sweden or Finns in Finland. The crude infant outcomes of Finns having given birth in Sweden were equal to those among Swedes in Sweden (except for the incidence of small for gestational age), but poorer than in Finland. Biological factors explained the differences between Finns in Sweden and Finland in being small for gestational age, and biological factors and smoking explained the difference in prematurity. The difference in low birth weight remained statistically significant (3.9% versus 3.6% among singletons). In conclusion, fertility trends followed the pattern prevailing in the resident country. The relatively good outcome of children whose mothers were born in Finland but who had given birth in Sweden can partly be explained by the healthy migrant effect.