According to attachment theorists, affect regulation and quality of attachment are closely linked. As a personality trait associated with deficits in the cognitive processing and regulation of affects, alexithymia has been hypothesized to correlate with insecure attachment. To test this hypothesis, we studied the relationships between alexithymia, adult attachment style, and retrospective memories of separation anxiety symptoms during childhood in 100 young men with clinically significant mood symptoms. The most common DSM-IV diagnosis (N = 72) was adjustment disorder with depressed mood, with anxiety, or with mixed anxiety and depressed mood. Each participant completed the Twenty-Item Toronto Alexithymia Scale (TAS-20), the Beck Depression Inventory (BDI), the state form of the State-Trait Anxiety Index (STAI), the Attachment Style Questionnaire (ASQ), the Relationship Questionnaire (RQ), and the Separation Anxiety Symptom Inventory (SASI). Alexithymic traits were more pronounced in those participants who had patterns of insecure attachment and who reported more severe symptoms of separation anxiety during childhood, independently of the severity of their current anxiety and depressive symptoms. Among the subgroup of participants with insecure attachment styles, those with preoccupied or fearful patterns had a higher prevalence of alexithymia (65% and 73%, respectively) than those with a dismissing pattern (36%). These data suggest a role for early developmental factors in the etiology of alexithymia.