This qualitative study examines how Latina girls' understanding of infidelity influences how they approach and interact with romantic partners. In-depth interviews with 24 Mexican American girls, ages 14 to 18, growing up in inner-city neighborhoods, formed the basis of this study. Although cheating was a major concern, most of the girls were more concerned with the emotional ramifications of being cheated on than any physical consequences. Fueled by a belief that most boys are "players," they became adept at identifying "red flags" that might indicate infidelity. The most frequently mentioned red flags were "Putting in the Time," "Adopting a Public Versus Private Persona," "Partner Seems Less Interested," "Being Secretive," and "Flirting with Other Girls." They also relied on electronic surveillance and peer warnings. Although the girls attempted to protect themselves, their reactions and behaviors were often constrained by a larger patriarchal structure outside their immediate control. Implications for gender-specific programs are discussed.