This study compared multiple characteristics of girls' and boys' vocabulary in 6 different linguistic communities--1 urban and 1 rural setting in each of 3 countries. Two hundred fifty-two mothers in Argentina, Italy, and the United States completed vocabulary checklists for their 20-month-old children. Individual variability was substantial within each linguistic community. Minimal cross-linguistic differences were found in children's vocabulary size; however, differences among languages in the composition of children's vocabularies appeared possibly related to cultural valuing of different categories of words. Ecological setting differences within cultures appeared in children's vocabulary size, even when the composition of children's vocabularies was examined: Children living in urban areas were reported by their mothers to say significantly more words than children living in rural areas, particularly for Argentine and U.S. children. Girls had consistently larger vocabularies than boys. These findings are discussed in terms of contextual and child factors that together influence first language learning. (Contains 4 footnotes and 5 tables.)