Background: The construct of alexithymia implies a deficit in symbolization for emotional, somatic, and mental states. However, the etiologic factors for alexithymia have not yet been fully elucidated. The present study investigated the use of mentalizing language, i.e. the utterance of internal states, from a developmental perspective according to attachment organization and disorganization. Methods: A longitudinal design across 4 time points was applied to a volunteer sample of 42 children. At 12 months, children were tested with the strange situation procedure, the standard measure of attachment at the optimal age, and attachment classifications were taken of videotapes. At ages 17, 23, 30 and 36 months, mother and child were observed in simplified separation episodes of 30 min duration. Transcripts of the sessions were subject to coding of internal state words. Results: During the investigated span, securely attached children rapidly acquired emotion, physiology, cognition and emotion-regulatory language, whereas insecurely attached and disorganized children either completely lacked internal state language or displayed a considerable time lag in the use of emotion and cognition vocabulary. Conclusion: The results raise the possibility that alexithymia might be a consequence of deficits in the development of internal state language in the context of insecure or disorganized childhood attachment relationships.