Social differences in late fetal death and infant mortality were examined in a population-based prospective study. All singletons born to Nordic citizens in Sweden 1985-86 were included, 185,156 births in all. The overall rates of late fetal death and infant mortality were 3.5 and 5.3 per 1000 respectively. Socio-economic status of the household (SES) and mothers' education were used as social indicators. Logistic regression analyses showed significant odds ratios between 1.3 and 1.8 for late fetal death for blue-collar workers and women with less than 12 years education. The analyses of neonatal mortality showed a U-shaped relationship: both unskilled blue-collar workers and high level white-collar workers had significant odds ratios (OR) as compared with intermediate level white-collar workers (OR = 1.5). Similar results were obtained when using the mothers' education as indicator of social status: 9 years education or less or 15 years or more were associated with significant higher mortality rates than 12 years education (OR = 1.6). An inverse relationship between social status and post-neonatal mortality was seen in the crude analysis. Mothers' education revealed more social differences than SES (crude OR = 2.0 and 1.5 respectively in the least privileged group). However, when adjusting for the effects of maternal age, parity and smoking, no significant odds ratios for the social variables were obtained.