Objective: To assess beliefs about the role of diet in cancer prevention among individuals considering genetic testing for Lynch Syndrome. Design: Family-centered, cascade recruitment; baseline assessment of a longitudinal study. Setting: Clinical research setting. Participants: Participants were 390 persons, ages 18 and older, including persons with a Lynch Syndrome-associated cancer and suspected of carrying a disease causing mutation, and relatives at risk for inheriting a previously identified mutation. Main Outcome Measures: Assess clustering of beliefs about the role of diet in cancer prevention and predictors of class membership. Analysis: Confirmatory factor analysis; 2-class factor mixture model with binary indicators; multilevel regression analyses, individuals nested within families. Results: Women endorsed a relationship between diet and cancer prevention more often than men (P less than 0.01). A 2-class model was used where Class 1 indicated less likely to link cancer to diet, and Class 2 indicated more likely. Factors associated with increased odds of membership in Class 1 expressed belief that nothing can prevent cancer (P less than 0.01) and fate attribution (P less than 0.01); Class 2 mentioned personal cancer history (P less than 0.05) and genetic knowledge (P less than 0.01). Conclusions and Implications: Identifying factors associated with a belief in cancer prevention through dietary behaviors can inform targeted interventions.