Someone who has a twin may be less likely to kill themselves, say researchers - pointing to the benefits of close family relationships.
Mirror image: Being a twin has its advantages
The suicide rate among more than 21,000 twins was 26% less for men and 31% lower for women.
It made no difference whether the twins were identical or non-identical.
Twins of all ages, from those born in 1870 to those born more recently showed exactly the same difference.
This is despite the fact that twins have a slightly higher than average rate of mental illness compared with the general population.
This should mean, in theory, a higher suicide rate than normal.
Researchers, from the Danish Twin Registry in Odense, wrote, in the British Medical Journal: "Our findings show exactly the opposite, further underscoring the importance of strong family ties."
However, while the presence of parents who stay together has often been cited by studies as a factor in reduced suicide rates, there are relatively few studies which examine whether siblings have an influence.
They wrote: "Twins represent an unique sibling relationship - they not only share the same family and social environment at least for the first part of their lives, but they also show a higher level of closeness both in terms of the numbers of years spent together before leaving the parental home and in the frequency of contacts afterwards."