In Finland as in many other countries, perinatal mortality is higher in those institutions having a higher level of care. To explain this phenomenon, mortality by weight groups was studied in different hospitals in the Central Hospital District of Helsinki in Finland in 1977-81. Among infants weighing less than 2 500 g, perinatal mortality was higher in the local hospital than in the university hospital, the higher mortality being due to the higher rate of stillborn infants. Among babies weighing over 2 500 g, the mortality was lower in local hospitals than in the university hospital. Further studies to explain the higher mortality of infants weighing over 2 500 g in the university hospital are needed.