In order to study pregnancy outcome for married versus unmarried mothers when controlling statistically for maternal age, educational level, socioeconomic status and income, a total of 93,800 firstborn singleton births in 1978-1982 were examined. The unmarried mothers were younger, less well educated and had a lower socioeconomic status than the married mothers. The stillbirth, neonatal, and postneonatal mortality rates were higher among offspring of unmarried mothers. After taking sociodemographic factors into account, marital status was found to be associated with postneonatal mortality. The adjusted odds ratio for postneonatal mortality was 1.5. Our results indicate the importance of marital status as a demographic risk factor even in a welfare society. There is a need to identify specific risk behaviours associated with the life styles of unmarried mothers. Hopefully our findings will provide information that can be used for future programmes of prevention, especially for the mother and her child during the first year of life.