In a longterm prospective study 20 extremely low birth weight (ELBW) infants with birth weight between 500 and 900 g (mean 755 +/- 109 g) and gestational age between 24 and 30 weeks (mean 26.2 +/- 1.8 w) were compared with 20 fullterm infants. This part of the study focuses on the impact on the family. Structured parental interviews were conducted in the postnatal period and at the end of the first year concerning the pregnancy, the delivery and the infant's health and behaviour during the first year of life. Questions about the parents' and siblings' reactions, physical symptoms and the strains on the husband-wife relationship were also asked. It was found that the mothers of the ELBW infants had more fertility problems, more physical symptoms during the pregnancy and the infant's first year of life. The birth of an ELBW infant caused crisis reactions in 85% of the mothers and 65% of the fathers. Fifty-eight per cent of the ELBW parents and 21% of the parents in the control group reported that the stress during the infant's first year had led to strains on the husband-wife relationship. It is evident that the birth of an ELBW infant had an impact on the whole family. However, we found no relationship between permanent neurological injuries in the infant and strong reactions in the family members. On the other hand, the parental relationship in the perinatal period seems to be of significance, as does the length of time the infant was hospitalized during its first year of life.