This study investigates the formal/informal voice used by native speakers in Cuernavaca, Mexico. Though listed as a very simple and obvious choice in many textbooks, usage is very subtle and complex. Social status, age, gender, and relationship are just some of the variables that dictate whether the speaker will be formal or informal in their discourse. Using William Labov’s sociolinguistic study of New York City as a model, the researchers observed and recorded unobtrusively the age, gender, and relationship of participants engaged in two person interactions in natural settings. After recording nearly 300 interactions, the researchers tallied the results and compared them to the preceding variables. The intent of this study was to discern a pattern for using either address choice. This study demonstrates the complexity of this grammatical feature, as well as provides valuable guidelines on when to use either voice.