Background. Early separation of a child from the mother has been considered a risk factor for later depression. We investigated the association between very early separation and depression in adulthood in a unique dataset.

Method. The index cohort consisted of 3020 subjects born in 1945–1965 in Finland, isolated from their family due to tuberculosis in the family and placed in special nurseries, immediately after birth, for an average time of 7 months. Those subjects alive at 1 January, 1971 were identified. For every index subject two reference subjects were chosen, the matching criteria being sex, year of birth and place of birth. Data on depression were obtained from the Finnish Hospital Discharge Register by the end of year 1998.

Results. In males, 4·2% of the index subjects and 2·6% (Adjusted Rate Ratio RR 1·7, 95% CI 1·3–2·3) of the reference subjects had been treated in hospital due to a depressive episode. In females the respective figures were 3·9% for index subjects and 3·6% (RR 1·1, 95% CI 0·8–1·5) for reference subjects.

Conclusions. The index subjects had an elevated risk for hospital treated depression in adulthood. One explanation may be that the very early temporal separation from the mother at birth may have unfavourable effects on later psychological development. On the other hand, separation from the parents at birth was not found to be strongly associated with severe adulthood depression.