This article compares the transformation of carnival celebrations in Buenos Aires, Argentina and Montevideo, Uruguay at the beginning of the 20th century. It argues that changes in carnival practices in the River Plate region was linked to the rise of a vacation culture in Montevideo. The article also assesses the historiography on Montevideo's carnival which has cast a negative light on the impact of modernization and the festival. In comparison to Buenos Aires', carnival in Montevideo was fomented by governmental regulation. Finally, the article examines the relationship between carnival and each of the city's African-descent populations.