Purpose: The objective of this study was to compare vocabulary size and composition in 2-year-olds learning Polish or English as measured by the Language Development Survey (LDS; Rescorla, 1989). Method: Participants were 199 Polish toddlers (M = 24.14 months, SD = 0.35) and 422 U.S. toddlers (M = 24.69 months, SD = 0.78). Results: Test-retest reliability was 0.92, internal consistency was 0.99, and concurrent validity was 0.55. Girls had higher vocabulary scores than boys. Mean LDS score was significantly lower in Polish than in English, and fewer Polish children had LDS scores >200 words. Also, more words were reported for <25% of the children, and fewer words were reported for =75% of the children, in Polish than in English. The cross-linguistic correlation for word frequencies was 0.44. Noun dominance was comparable in the two languages, and 55 cross-linguistic word matches were found among the top 100 words. Although more Polish than U.S. children had <50 words (18.1% vs. 8.3%), children with <50 words and those with =50 words were generally acquiring the same words. Conclusions: Vocabulary acquisition appeared to be slower in Polish than in English, probably because of the complexity of the language. However, the languages were very similar with respect to vocabulary composition findings.