Sub-optimal language development is associated with the metabolic disorder galactosaemia (GAL). Some children with GAL are identified with language impairment from the initial stages of language learning, but a subset of children may exhibit disrupted developmental gains in speech and language skill after a period of age-appropriate skill development. The developmental trajectory of communicative skills in a female with GAL who at 18 months of age presented with age-appropriate skills is presented. Monitoring over an 18-month period indicated appropriate developmental pace on all measures, but receptive vocabulary development is developing at a lower level of functioning. Her below-average vocabulary skills coupled with the risk of emerging skill deficits concomitant with ongoing disruptions to central nervous system maturation associated with GAL suggests an increased risk of emergent skill deficits. Maturation of language capabilities is ongoing; therefore age at assessment may be critical to the timely documentation of lack of skill progression.