Differences in the ways male and female patients confront their illness after cardiac surgery may contribute to previously observed gender differences in the outcomes of cardiac rehabilitation. The aim of this cross-sectional study was to verify whether there are gender-related differences in illness behavior (IB) soon after cardiac surgery and before entering cardiac rehabilitation. Patients (N = 1323) completed the IB Questionnaire and Hospital Anxiety and Depression Scale (HADS) 9 ± 5 (mean ± SD) days after cardiac surgery. The scores were tested for gender differences in score distributions (Mann-Whitney U test) and in prevalence of clinically relevant scores (the Pearson χ² test). Multivariate regression analyses were made with IB Questionnaire and HADS scores as independent variables, and gender, age, education, marital status, and type of surgery as predictors. Denial was significantly (P < .01) prevalent among the men (3.6 ± 1.4) versus women (3.2 ± 1.6), whereas disease conviction (men = 2.1 ± 1.5, women = 2.5 ± 1.6), dysphoria (men = 1.5 ± 1.5, women = 2.0 ± 1.6), anxiety (men = 6.0 ± 3.6, women = 6.9 ± 3.9), and depression (men = 5.3 ± 3.8, women = 6.5 ± 4.0) were significantly more prevalent among women. The prevalences of clinically relevant scores for disease conviction, anxiety, and depression were also significantly higher in women. Multivariate analysis showed that gender predicted these scores even after the removal of confounders. Gender differences exist in denial, disease conviction, and dysphoria, probably depending on the culturally assigned roles of men and women. As these aspects of IB may compromise treatment compliance and the quality of life, the efficacy of cardiac rehabilitation programs might be improved taking into account the different prevalences in men and women.