Mothers of twins, as compared with mothers of singletons, are taller, and for a given height are heavier; they have slightly earlier menarche and menopause. Our recent studies have shown that mothers of DZ twins are at greater risk of cancer of the pancreas (but not for cancers of other sites), as well as of death due to diabetes, other endocrine diseases, and allergies. These findings are consistent with the clinical and epidemiological literature. We have also found that singleton siblings of twins are slightly heavier at birth than children born into sibships consisting of singletons only. The need for further research on the characteristics and long-term health of mothers of twins is indicated.