Early triadic interaction, the reciprocal action between mother-father-child, is described in the family of a girl diagnosed with autistic spectrum disorder (DSM 299.00) and learning difficulties at seven years. By chance, the family participated in a longitudinal study examining triadic interaction in 20 Swedish families using the Lausanne Triadic Play method. Quantitative and qualitative observations were made when the children were three, nine, 18 and 48 months of age. Compared with the other families, deviation was noted in early triadic synchronization, most clearly when the girl was nine months old. At three months, the girl took more turns and participated in more turn-taking sequences than the other children. However, at nine months, she gave more attention to objects. At 18 months, she had less eye contact with her parents and less shared focus and at 48 months her language skills were poorly developed. The mother showed more frequent contributions and more frequent turns at the two observations during infancy. The father showed deviations in attention to the child and affirmation at nine months and negative vocalization at 18 months. These findings are discussed in terms of their importance with regard to early intervention. Assessment of the family interaction using home observations seems to be of special importance. (Contains 3 tables and 3 figures.)