Improvements in combining obstetrics and neonatology led to a trend to intervene earlier in premature babies born before the 33rd week of gestational age. The enquiry that was carried out in 1985 in the Paris geographical region had as its objective to assess on the one part how many premature deliveries occurred between the 25th and 33rd week of amenorrhea and on the other hand what happened in the short term to the infants born from these pregnancies, i.e., their mortality; and for those who survived, their quality of life. The study was carried out on a representative sample of the deliveries in 1985 in the four departments of the Paris region--Paris and the three departments of the Petite Couronne--where half of all deliveries were assessed. The enquiry covered 53,430 deliveries for which the overall prematurity rate was 4.5%, and those deliveries that occurred before 33 weeks of gestational age constituted 1.0% (539 babies). Twenty children were lost for follow-up after a year. This was 4.9% of the live births and 6.3% of the live children who left the neonatology centres. At 2 years of age, the numbers that were not followed up were eventually 24, which was 5.8% of live births and 7.6% of those that left the centres of neonatology. The results show a very high rate of antepartum mortality but also of mortality during and after labour. Only 379 infants out of the 539 (70%) were transferred into special care baby units. By 1 year of age, the survivors were 57% of the total number of deliveries and 75% of the live births and 82% of those transferred to the special units. As far as concerned those that were live born, the survival rate at the age of 1 year varied considerably according to the duration of the pregnancy. The number of those that survived a pregnancy of less than 27 weeks was low (31%). It was, at 28 weeks, 53%. This is the age where births have to be registered. It reached 87% of the live births that occurred at 32 weeks. One has to point out that there is no statistically significant difference between 27 and 28 weeks of gestation. Whereas there is a significant difference (p less than 0.05) with those delivered at 29 weeks (75%). 80% of those 291 infants that were examined at 1 year of age were considered to be normal as far as psychomotor and sensorial behaviour was concerned.(ABSTRACT TRUNCATED AT 400 WORDS)