There is widespread agreement with in the field of early childhood education that vocabulary is important to literacy achievement and that reading aloud can support vocabulary growth. However, there are unexplored and significant problems with the ways we assess young children's vocabulary learning from read-alouds. This paper critically reviews the forms of vocabulary assessment commonly used with young children, examining the benefits and drawbacks of each. This review found: (a) general vocabulary measures are not practical, meaningful measures for vocabulary learning of specific words from books read aloud, (b) researcher-developed measures for specific words from books read aloud that mimic normed general vocabulary measures include serious threats to validity and reliability, and (c) other forms of measurement, such as soliciting definitions from children, are difficult to score reliably. This critical review of existing vocabulary assessments of word learning from read-alouds concludes that researchers and practitioners should carefully consider their needs for assessment data so as to choose, design and balance the uses of assessments to meet their needs for meaningful, reliable data.