Attachment was assessed in toddlers with Autistic Disorder (n = 20), Pervasive Developmental Disorder (n = 14), Mental Retardation (n = 12), Language Development Disorder (n = 16), and a non-clinical comparison group (n = 18), using the Strange Situation Procedure (SSP). Children in the clinical groups were more often disorganized and less often securely attached. Severity of autism was associated with more attachment insecurity, and lower developmental level increased the chance for disorganized attachment. Attachment disorganization was related to increased heart rate during the SSP. Controlling for basal cortisol and developmental level, more autistic symptoms predicted lower cortisol responses to the SSP. The findings support the importance of disorganized attachment for children with autism.