Mexican-descent women are at particular risk of late-stage breast cancer diagnosis by being the least likely of the major U.S. Hispanic subgroups to undergo breast cancer screening. This grounded theory study investigated how cultural health beliefs regarding the causes and nature of breast cancer influence women's decision to participate in screening. Thirty-four women (age 49 to 81) were interviewed in five focus groups using theoretical sampling across levels of acculturation and socioeconomic status. Analysis of the most prevalent cultural health beliefs led to a discovery that the core problem Mexican-descent women face is that they perceive there is no reason to participate in breast cancer screening when they are "feeling healthy." In addition, women who subjectively and cognitively feel healthy and otherwise have no evidence of illness according to their cultural health beliefs are unlikely to risk feeling ill rather than healthy by seeking to discover breast cancer through screening.