The author, herself a mother of twins, reviews research on exceptional twins. She considers reasons for fascination with twins and comments upon important advances in technology. Current research in Indianapolis to measure cognitive, perceptual, personality, and chromosome patterns of twins is described. Differences in the makeup of identical and fraternal twins are considered, as are specific dangers that can affect twins prenatally and perinatally. She describes experiences of parents of exceptional twins and discusses the feelings of the nonhandicapped twin. Sex differences in terms of vulnerability to disorders are noted, and the effect of family configuration on intelligence is addressed. Prevention through better medical care and nutrition is suggested. (CL)