This case study provides a first exploratory study on the early Flemish Sign Language acquisition of a deaf infant from the perspective of Halliday’s Systemic Functional Theory. It highlights some remarkable aspects of sign language acquisition with respect to interpersonal interaction between the child and its mother. The free play interactions of the Deaf mother and her moderately deaf daughter were recorded when the child was 6, 9, 12, 18 and 24 months old. These interactions were annotated in ELAN and transcribed in view of the analysis adapting Systemic Functional Linguistics. The analysis indicates that the early sign language development of the child chronologically correlates with Halliday’s descriptions of the universal functions of language. The infant’s first lexical signs appeared at 12 months. The child produced one-sign utterances (12 months and older), one-sign utterances along with a pointing sign (18 months and older) and two-sign utterances (24 months). The mother integrated attentional strategies to redirect the child’s attention. She also adopted techniques that are appropriate for child-directed signing, i.e. questions, recasts and expansions.