Two sibs and their mother were affected with a syndrome like the Rubinstein-Taybi syndrome. All three individuals had broad terminal phalanges of the thumbs and great toes, antimongoloid slant of the palpebral fissures, and characteristic facial appearance with beaked noses. Four sibs of the mother had broad thumbs, suggesting a familial pattern. So far there has been no report of dominant transmission of the Rubinstein-Taybi syndrome. This family bears close resemblance to the Rubinstein-Taybi syndrome, which is transmitted as an autosomal or X-linked dominant trait. Inasmuch as the expressivity of the syndrome may be variable, we propose that a thorough family investigation is indicated in all apparently sporadic cases of Rubinstein-Taybi syndrome. Familial cases may be more common than realized and require appropriate genetic counseling.