The infant mortality rate in North Rhine Westphalia (NRW), the most populous West German state, has continuously been around 10% higher than the German national average in the post-war period. Using white singleton data from the US 1980 National Infant Mortality Surveillance project (NIMS) and similar 1980/1981 data from NRW we compared infant mortality by birthweight and cause to describe the distribution of excess mortality in NRW. The US infant mortality rate was 8.7 deaths per 1,000 live births, compared with 13.1/1,000 for NRW (rate difference: 4.3/1,000). Of the 4.3/1,000 overall rate difference, 1.9/1,000 was attributable to neonatal deaths, 2.4/1,000 to postneonatal deaths. A major proportion, 2.0/1,000, of the overall rate difference of 4.3/1,000 was attributable to normal birthweight deaths postneonatally. 0.85/1,000 of this 2.0/1,000 rate difference was attributable to SIDS, 0.44/1,000 to external causes and 0.42/1,000 to infections.