In this study, new evidence is presented of marked sex differences in the distribution of insecure attachment patterns in middle childhood. Attachment was assessed with the Manchester Child Attachment Story Task (MCAST) in a sample of 122 Italian 7-year-olds. The four-way distribution of attachment patterns was significantly unbalanced, with insecure boys more often avoidant (27%) than ambivalent (2%), and insecure girls more often ambivalent (25%) than avoidant (4%). In addition, boys were rated as more severely disorganized than girls on a continuous disorganization score. A survey of previous literature strongly collaborates these findings, showing that similar attachment distributions have been obtained cross-culturally (US, Canada, and Israel) in nearly all of the (relatively few) studies in which children's sex had been taken into account. It is argued that sex biases in attachment avoidance/ambivalence become apparent starting at about 6–7 years, in contrast with the lack of sex-related effects in infancy and early childhood, and probably anticipate the pattern of sex differences found in adults with romantic attachment questionnaires.