A forced-choice reaction time (RT) task was used to assess the filtering component of selective attention in mental-age (MA) matched groups of persons with autism (n = 12), organic mental retardation (n = 32), familial mental retardation (n = 30), and no handicap (n = 34). Conditions varied with regard to the presence or absence of a window and number (zero, two or four) and location of distractors. The RTs of the persons with autism improved relative to the other groups in the presence of the window without distractors, but this effect was negated when distractors were also presented. The performance of the persons with autism was the most impaired in the presence of distractors. These findings represent preliminary behavioral evidence of an inefficient attentional lens among persons with autism.