Sensory disabilities may limit a person's development of intersubjectivity, that is, the awareness of self and other, which develops in conjunction with interpersonal communication. This study used intersubjectivity theory to test a new intervention called the High-Quality Communication (HQC) intervention for its effects on a young adult with congenital deafblindness and a developmental age of between 1.5 and 4 years. Three of his social partners were trained to support attunement and meaning making with him through education and video feedback. This study measured seven observation categories at three layers of intersubjective development during a baseline and two intervention phases: dyadic interaction, shared emotion, referential communication, meaning negotiation, shared meaning, declarative communication, and shared past experience. The participant's use of conventional communication was included as an additional category. Effects were observed in all observation categories from the baseline to the intervention phases. Further study of the effectiveness of the HQC intervention is recommended to test whether effects generalize across people and settings.