This study aims to explore the genetic and environmental contributions to autistic-like behaviors in a general population sample of toddlers. In a classic twin study of 313 same-sex, 2-year-old twin pairs, autistic-like behaviors were assessed via parent ratings on the pervasive developmental problems subscale of the Child Behavior Checklist and observationally using tester ratings on the orientation/engagement subscale of the Behavior Rating Scale. Analyses show moderate, significant heritabilities for both measures of autistic-like behaviors, as well as modest, but significant shared environmental effects. These genetic and environmental influences overlap greatly between the two measures. Autistic-like behaviors in 2-year-old twins are largely genetic in etiology, but are also influenced by a shared environmental component at this age. This is the first study to examine the etiology of such behaviors in a sample of toddlers, thus providing novel information which could guide future research on genetic and environmental factors that affect these behaviors.