Following Main and Hesse's hypothesis, several investigators have affirmed that frightened/frightening (FR) as well as particular atypical maternal behaviors are associated with infant disorganized and adult unresolved attachment. Here, for the first time, FR behavior was observed in (a) middle-class father-infant (n = 25) and independent mother-infant dyads (n = 50) and (b) a brief laboratory play session. In addition, relations between disorganization, unresolved attachment, and the six FR system subscales were explored. Paternal and maternal overall FR behavior was related to infant disorganization (n = 75, phi = .61, p < .001), and for a subsample where Adult Attachment Interviews were available (n = 32), to unresolved adult attachment (phi = .59, p < .001). At the subscale level, disorganized-FR behaviors were related to infant disorganization, but only for mother-infant dyads. Across the whole sample, both dissociative-FR and threatening-FR subscales were associated with infant disorganization. The dissociative-FR subscale emerged as the central predictor of infant disorganization and was the only subscale significantly related to unresolved attachment. The appearance of FR behavior in this 18-min play procedure suggests that FR probably occurs more frequently than previously suspected. The possible role of dissociative processes in unresolved adult attachment, disorganized attachment, and FR parental behavior is discussed.