To examine the external validity of DSM-IV childhood disintegrative disorder (CDD), 10 children (M = 8.2 yrs) with CDD and 152 gender- and age-matched children with autistic disorder (AD) were compared on 24 variables. The CDD children had a significantly higher rate of epilepsy, significantly less uneven intellectual functioning, and a tendency of greater abnormality in auditory responsiveness than AD children, to validate CDD externally. Their short-term outcome, as shown in the degree of retardation, was not worse than the AD children, which is in disagreement with previous studies reporting worse outcomes in CDD than autism. These results need to be verified by a long-term prospective study that compares CDD and AD patients from infancy.