BACKGROUND After unification, the gap in infant mortality rates between the two parts of Germany widened until 1996 before converging. The reasons for these changes have not, so far, been apparent. OBJECTIVES To investigate trends in neonatal and postneonatal mortality in the eastern (the new Länder) and western (the old Länder) part of Germany after unification in 1990 and to identify the scope for further improvement. DESIGN Examination of trends in birth weights, birth weight specific neonatal mortality and cause specific postneonatal mortality in the two parts of Germany from 1990 to 1996 and 1997 by analysing routinely available vital statistics data. RESULTS In both parts of Germany, neonatal mortality fell considerably, by 33 per cent in the east and 17 per cent in the west, from 4.5 and 3.5 per thousand live births in 1990 to 3.0 and 2.9 in 1997, respectively. This was attributable to an improvement in survival of infants at all birth weights but especially among those with very low birth weights, accounting for an estimated 83 to 85 per cent of the overall improvement. The birth weight distribution showed a slight worsening in the new and the old Länder with an increase in the proportion of those under 1500 g and, in the east, a 24 per cent increase in the proportion of high birthweight infants of 4000 and more grams. Trends in postneonatal mortality revealed a worsening of about 32 per cent in the east from 1990 to 1991 followed by a decline of over 50 per cent up to 1997, leading to comparable mortality rates of 1.8 per thousand live births in the east and 2.0 in the west. While both parts experienced a decrease of 40 to 48 per cent in deaths from all diseases, the decline in deaths because of accidents and injuries was markedly higher in the new Länder although they are still exceeding the western rate by 3.7 per 100 000 live births in 1997. CONCLUSIONS Since unification, the two parts of Germany underwent a complex process that has led finally to convergence of parameters of infant health that are most likely to have been because of improvements in the quality of perinatal care. To improve infant mortality in Germany, policy measures should focus on preventive rather than curative measures as the proportion of very low birthweight babies is increasing in both parts of Germany.