In this study vocabulary development of a sample of 42 Italian children was evaluated through monthly administration of the Italian version of the CDI. Data collection started at 1;0–1;1 for 32 children and at 1;3–1;4 for the remaining subjects and continued until children's vocabulary reached 200 words. At fixed stages of vocabulary size (50, 100 and 200 words), individual differences in percentile scores and vocabulary composition were examined. Individual growth curves were analysed in order to verify the presence of a vocabulary spurt and the type of lexical items which contributed most to rapid acceleration in vocabulary growth.

Stylistic differences in vocabulary composition were examined regarding the ‘referential–expressive’ distinction, controlling vocabulary size. Data have shown that general trends in vocabulary development are quite similar to those obtained for other languages using CDI adaptations. Moreover, all children in this sample eventually exhibited a vocabulary spurt, even if some can be defined as ‘late spurters’. The type of lexical items which are learned during the spurt depend on both infant vocabulary size and referential score. About 28% of infants in this sample were defined ‘referential’ when their vocabulary size was about 50 words, but the stylistic differences disappeared at the 100- and 200-word stages.

Composition of vocabulary did not differ in relation to precocity in reaching different stages of vocabulary development. The only exception was that infants who reached the 50-word stage first also had a vocabulary with a lower proportion of function words.