The associations between vocabulary growth and reading development were examined longitudinally for a representative sample of Dutch children throughout the elementary school period. Data on basic and advanced vocabulary, word decoding, and reading comprehension were collected across the different grades. The results showed significant progress on all of the measures over time. The stability of the vocabulary measures was high, which shows a great deal of continuity in both the basic and advanced vocabularies of the children. Beginning vocabulary was found to predict early word decoding and reading comprehension as was predicted from the lexical restructuring hypothesis. From second grade on, word decoding predicted later vocabulary development. Moreover, a reciprocal relationship between the children's advanced vocabulary and reading comprehension was detected. The data provide support for the lexical quality hypothesis as knowledge of word forms and word meanings predicts the development of reading comprehension. (Contains 1 table and 2 figures.)