Early intensive behavioral intervention (EIBI) is often recommended for children with Pervasive Developmental Disorders (PDD). It is an empirically supported treatment designed to address the core symptoms of autism including language delays, social and play skills, and restricted and repetitive behaviors as well as other related deficits in cognition and adaptive behavior. Though there are a growing number of research studies supporting EIBI, many questions remain about the nature and stability of best outcomes. The current study provides case descriptions of eight children previously diagnosed with an autism spectrum disorder and mental retardation who, after EIBI treatment, no longer met behavioral criteria for mental retardation or a PDD. The average gain in IQ standard scores was 34.6 ( ± 13.2) points; and, the average gain in adaptive behavior standard scores was 43 ( ± 25.3) points. Nonverbal IQ standard scores (mean = 93 ± 12.6) and academic achievement standard scores (mean = 105.3 ± 18.7) ended within the average range. Language skills remained impaired for seven children. The cases support findings of other researchers that learning recovery in autism and PDD is possible and may be related to intensive behavioral treatment. Individual differences in response to EIBI treatment are discussed. Copyright © 2006 John Wiley & Sons, Ltd.