Receptive vocabulary is an important aspect of cognitive functioning. It appears to be a relative strength with respect to language for individuals with Down syndrome (DS) but little is known about its development as individuals mature. This study was designed to establish the developmental trajectory of receptive language development in individuals with DS from early childhood to midadulthood. Two hundred and six individuals with DS provided Peabody Picture Vocabulary Test (PPVT) scores on 957 occasions, spanning ages from 2 years 7 months to 29 years 7 months. Latent growth curve models were used to establish the trajectory of receptive vocabulary. Gender, maternal education, cohort, and nonverbal intellectual ability were used as predictors of rate of development. Receptive vocabulary was found to increase until around 20 years of age when performance on the PPVT began to deteriorate. The only variable measured that was associated with PPVT performance was nonverbal ability. The rate of increase in receptive vocabulary in individuals with DS across the childhood and adolescent period appears to be slower than for those who are developing typically, and the expected influence of maternal education was not found. The small number of participants contributing data in the older ages included in this study means that the apparent decline in receptive vocabulary scores needs to be interpreted cautiously.