The author combines the points of view of geneticist and psychologist in these unusually sensitive observations of personal relationships. Sixty-two pairs of same-sexed normal twins between the ages of twelve and fifteen, thirty-six uniovular and twenty-six binovular, were studied by interviews with the twins and their parents and by obtaining reports from clinics and schools. Uniovular twins with mild emotional disturbance resemble each other in kind of symptom and in outstanding personality characteristics more closely than do binovular twins. This fact suggests that some persons are more vulnerable than others to the minor stresses in life for genetic reasons. The severity of the disturbance, however, appears to depend on environmental factors, since twins of identical genetic structure do not always suffer from the same complaint in the same degree.