Main and Hesse's (1990) model in which frightening (threatening, frightened, or dissociated) parental behavior explains why infants of parents with unresolved loss develop disorganized attachment relationships was tested. Unresolved loss using the Adult Attachment Interview in a nonclinical middle-class sample of 85 mothers who had experienced the loss of someone important was assessed. Disorganized attachment was examined in the Strange Situation. Parental behavior was recorded during 22-hr home visits. The model applied to mothers with currently insecure attachment representations. Secure mothers with unresolved loss displayed less frightening behavior than other mothers, and unresolved loss in secure mothers did not predict disorganized attachment of their infants. Frightening behavior predicted infant disorganized attachment irrespective of maternal security.