Autism is a serious psychological disorder with onset in early childhood. Autistic children show minimal emotional attachment, absent or abnormal speech, retarded IQ, ritualistic behaviors, ag- gression, and self-injury. The prognosis is very poor, and medical therapies have not proven effective. This article reports the results of behavior modification treatment for two groups of similarly consti- tuted, young autistic children. Follow-up data from an intensive, long-term experimental treatment group (n = 19) showed that 47% achieved normal intellectual and educational functioning, with normal-range IQ scores and successful first grade performance in public schools. Another 40% were mildly retarded and assigned to special classes for the language delayed, and only 10% were pro- foundly retarded and assigned to classes for the autistic/retarded. In contrast, only 2% of the control- group children (n = 40) achieved normal educational and intellectual functioning; 45% were mildly retarded and placed in language-delayed classes, and 53% were severely retarded and placed in autis- tic/retarded classes. Kanner (1943) defined autistic children as children who ex- hibit (a) serious failure to develop relationships with other peo- ple before 30 months of age, (b) problems in development of normal language, (c) ritualistic and obsessional behaviors ("in- sistence on sameness"), and (d) potential for normal intelli- gence. A more complete behavioral definition has been pro- vided elsewhere (Lovaas, Koegel, Simmons, & Long, 1973). The etiology of autism is not known, and the outcome is very poor. In a follow-up study on young autistic children, Rutter (1970) reported that only 1.5% of his group (n = 63) had achieved nor- mat functioning. About 35% showed fair or good adjustment, usually required some degree of supervision, experienced some diffaculties with people, had no personal friends, and showed minor oddities of behavior. The majority (more than 60%) re- mained severely handicapped and were living in hospitals for mentally retarded or psychotic individuals or in other protective settings. Initial IQ scores appeared stable over time. Other stud- ies (Brown, 1969; DeMyer et al., 1973; Eisenberg, 1956; Free-