Abstract: Previous research has established that the pattern of an infant's attachment is likely to be related to his/her parent's state of mind as demonstrated on the Adult Attachment Interview (AAI), and related as well to the kind of interactions the infant has experienced with that parent. In responding to the AAI, parents of “disorganized” infants are disproportionately likely to show that they have been unable to “resolve” prior experiences of trauma and loss, and/or that their general model of relationships is “hostile/helpless.” These atypical states of mind are thought to affect how the parent responds to the infant's attachment behavior, inducing the parent to behave in frightening or otherwise atypical ways and thus making it difficult or impossible for the infant to maintain an organized pattern of attachment. The present project tested this hypothesis about the relationship of atypical parental behavior to parental state of mind and infant disorganization in a high-risk sample (N = 149) which included a large number of substance-dependent mothers and mothers who had experienced significant trauma. The study employed the AMBIANCE (Atypical Maternal Behavior Instrument for Assessment and Classification), which measures a broad range of maternal behaviors thought potentially disorganizing to infants' attachment. Results showed that atypical maternal behavior was more strongly related to the resistant/ambivalent category of infant attachment, both organized and disorganized, than it was to disorganization. Higher AMBIANCE scores were also found related to greater indications of hostile/helpless state of mind, but not to unresolved states of mind. Hostile/helpless state of mind was independently related to infant disorganization after controlling for contextual risk factors (poverty, low educational levels, single motherhood, teen motherhood, and large numbers of children). The Helpless/Fearful subtype of maternal behavior was more strongly related to infant disorganization than was the Intrusive/Self-referential/Mixed subtype, but it was not differentially related to the Helpless/Fearful state of mind. Results are discussed in relation to past findings and suggestions for future research.