Young adult (YA) cancer survivors are at increased risk for chronic diseases and face age-dependent stressors that may hinder their ability to maintain healthy lifestyle behaviors. This study examined associations between reported mental health, eating beliefs, and health behaviors in YA cancer survivors. YA cancer survivors aged 18-39 years (n = 225) completed a self-administered REDCap® survey, including the Perceived Stress Scale 10, PROMIS® Anxiety and Depression, Eating Beliefs Questionnaire, National Health and Nutrition Examination Survey Dietary Screener Questionnaire, Godin-Shephard Leisure-Time Physical Activity Questionnaire, and demographic and diagnosis-related questions. Descriptive statistics, bivariate analyses, and multiple linear regression were performed. Participants were mean 31.3 years old and 3.7 years post-treatment; 77.3% were women. Most participants reported White (78%) or Black or African American (11.2%) race and non-Hispanic ethnicity (84%). Adjusting for covariates, perceived stress, anxiety, and depression were associated with increased added sugar intake (p < 0.001) and eating beliefs (p < 0.001). Perceived stress and depression were associated with reduced vegetable intake (p < 0.05). There were no associations with fruit intake or physical activity in the adjusted models. Health behavior interventions for this population may address psychosocial needs by including a stress management or mind-body component. Further research including direct measures of health behaviors is warranted.