In order to examine several aspects related to the natural history of the Rubinstein-Taybi syndrome, we performed a questionnaire study of 50 patients who had been diagnosed with the condition. The cases were ascertained through a national parent support group and all of the individuals had been reared at home. The most frequent problems encountered were inadequate weight gain in infancy, eye problems, dental abnormalities, congenital heart defects, urinary tract problems, and severe constipation. These medical disorders and others resulted in approximately 10 times the average number of hospitalizations and surgeries as the general population of children. None of the 91 sibs of our study group were affected with the condition. Thirty-seven patients had undergone psychological testing with an average IQ of 51 and a range of 30 to 79. Timing for the attainment of various developmental stages was also determined. Individuals with Rubinstein-Taybi syndrome were found to have particular difficulty with expressive speech skills. Indexes for maladaptive behavior were calculated showing that approximately 10% of patients had significant behavior problems.