ABSTRACT: Cross-sectional methodologies have revealed age-related deterioration in cognitive performance, reflecting progressive neurodegenerative change in a minority of children and adolescents with classic galactosemia (GAL). The application of longitudinal methodologies sensitive to age-related changes at the individual level is needed to determine the extent of any possible decline in function in children with GAL. The authors report on the developmental language outcomes of a 9-year-old female with GAL through an examination of her language development over a 7-year period using a performance tracking system based on the use of raw performance scores required for attainment at the 50th percentile for age. Raw scores typically increase systematically over time and are thus more sensitive to developmental changes. Results suggest that there was no decline in the child’s language skills over the course of the investigation. For the case presented, the use of raw scores offered a means of examining the child’s patterns of individual change, which revealed stable language skills over the period of monitoring, perhaps indicating a stable disease process for this particular child. The authors propose this descriptive application of raw performance scores that offers a means to determine neurodevelopmental outcomes in the disorder.