Method: Sixteen studies on attachment in children with autism were reviewed, and ten studies with data on observed attachment security (N = 287) were included in a quantitative meta-analysis. Results: Despite the impairments of children with autism in reciprocal social interaction, the majority of the studies found evidence for attachment behaviours in these children. In four samples using the Strange Situation procedure the average percentage of secure attachments amounted to 53% (n = 72). Meta-analytic results showed that children with autism were significantly less securely attached to their parents than comparison children, and the combined effect size for this difference was moderate (r = 0.24). Children with autism displayed less attachment security than comparisons without autism, but this difference disappeared in samples with children with higher mental development, and in samples in which autism was mixed with less severe symptoms of autistic spectrum disorders. Conclusions: It is concluded that attachment security is compatible with autism, and can be assessed with Strange Situation type of procedures. The co-morbidity of autism and mental retardation appears to be associated with attachment insecurity.