Purpose: This study reexamines the claim that difficulty forming memories of words comprising uncommon sound sequences (i.e., low phonological neighborhood density words) is a determinant of delayed expressive vocabulary development (e.g., Stokes, 2014). Method: We modeled communicative development inventory data from (N = 442) 18-month-old children, with expressive lexicon sizes between 0 and 517 words (Mdn = 84). We fitted a Bayesian regression model in which the production of each communicative inventory word (N = 680) by each child was predicted by interactions between that child's expressive lexicon size and the word's (a) phonological neighborhood density, (b) frequency in child-directed speech, (c) length, (d) babiness, and (e) concreteness. Results: Children with larger expressive lexicons were more likely to produce words comprising uncommon sound sequences than age-matched children with smaller lexicons. However, the magnitude of the interaction between expressive lexicon size and phonological neighborhood density was modest relative to interactions between expressive lexicon size and word frequency, length, babiness, and concreteness. Conclusion: Emphasis on a difficulty with the memorization of low--neighborhood density words as a determinant of slow vocabulary growth may be unwarranted, and the current evidence base in this direction is not robust enough to strongly support the development of possible interventions for late talkers.