There is more and more research of lexical development in the Croatian language, but there are still parts of that development that have not been sufficiently researched. That is why the aim of this paper is to investigate the lexical development of children from the first word to the sixteenth month. More precisely, this paper identifies the first word class and semantic categories and the dominant word class and semantic categories at the age of 16 months in the expressive vocabulary of children whose mother language is Croatian. The data required for this research were collected using the Short version of the Communication Development Scale - Word and Gesture subscale (8 - 16 months) which is in the process of standardization. Data from the scale which show active and passive vocabulary of the child were used. They are taken from the finished database created during the standardization process of the mentioned scale. Random selection based on age and gender selected 70 respondents. 35 of them at the age of 12 months and 35 at the age of 16 months. After a statistical analysis of the parents' report on children's productive vocabulary, the obtained results show within children at the age of 12 months, the most frequent word class is a noun, which is in line with research in other languages. At that age, children produce the most words that belong to the semantic category of people, followed by other categories that are part of their daily activities. At the age of 16 months, most frequent are nouns as well, followed by exclamations. The sudden rise of the verb is interesting. The results of processing semantic categories at that age show that the semantic category of people is still the most frequent. No major changes are found in the dominant word class and semantic categories between 12 months old and 16 months old children. This can be attributed to the slow acquisition of new words all the way to the vocabulary spurt beginning around the eighteenth month.