Institutional care has been shown to lead to insecure and disorganized attachments and indiscriminate friendliness. Some children, however, are surprisingly resilient to the adverse environment. Here the protective role of the long variant of the serotonin receptor gene (5HTT) is explored in a small hypothesis-generating study of 37 Ukrainian preschoolers reared in institutional settings or in their biological families. Attachment was observed with the Strange Situation Procedure, and indiscriminate social behavior was assessed in a semistructured interview with the caregiver. We found a moderating role of 5HTT for the association between adverse environment and attachment disorganization. Children with the ss or sl genotyope showed more attachment disorganization and less attachment security when they grew up in an institution compared to children who lived in a family, but children who were homozygous for the l allele appeared to be protected against the adverse institutional environment on attachment. We conclude that not all children may be equally vulnerable to extremely adverse rearing experiences. (Contains 2 tables and 1 figure.)