Course of pregnancy, family history and genetics were evaluated in 257 children with spina bifida and compared with 537 non-malformed controls investigated under the same criteria. Birth data exhibited a significant seasonality with a maximum in January and a minimum in July which differed from the average distribution of birth data in Bavaria (maximum April, minimum October). The total number of pregnancy disturbances was 60.6% in mothers of spina bifida children, whereas this figure amounted to 30.1% in mothers of the control group. This high incidence of pregnancy disturbances in spina bifida was due to a high rate of diseases (6 times above controls) and drugs (6 times above controls) during early pregnancy. In 22.9% of children with spina bifida malformed relatives were found, whereas this was the case in only 6.4% of the children of the non-malformed control group. Not only malformations of the central nervous system but also malformations of other organ systems were found to be increased in relatives. This is a pointer not only to genetic influences as well-known aetiological factor, but also towards a generally higher susceptibility to malformation genesis in a relatively small group of persons. Risk of recurrence was 0.5% if one parent was affected and 4% if a sibling was affected.