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Information on personnel, equipment and care facilities a t all maternity institutions has been related to the perinatd mortality among all single births in Norway, 19617-1973. There was a total of 454,358 single births during this seven year period which comprised the study data set. An obstetric score based on personnel and equipment as defined in a previous study has been used to divide the country into three groups of counties, with low, medium and high obstetric scores. Perinatal, fetal and early neonatal (less than seven days) mortality rates specific to birth weight categories in 500 gram intervals have been compared between the county groups. Significant differences were found in the mortality rates between the group of counties with low obstetric score and the two other groups. There h both a relative and absolute increased difference in mortality for births weighing 3000 grams or more compared to births less than 3000 grams. The major component in the perinatal mortality difference is due to a difference between the low and higher obstetric score county groups in the early neonatal mortality rates. Time trends indicate that the relative differences in perinatal mortality are not decreasing over the seven year period, but rather, have increased slightly. Potential differences in the populations at risk in the three county groups are discusses. An adjustment was made to eliminate the effects of some potential confounding variables, namely high parity and maternal age and illegitimacy, without basically changing the results.