This article examined the relationship between type C personality and the development of breast cancer. Two characteristics has been reported consistenly in the literarature: suppression of negative emotions (or rationality) and need for harmony. The Rationality/ Emotional Defensiveness and Need for Harmony Scales (Spielberg, 1988) were administered to 480 women (20-68 years old) whom was examined for breast cancer screening. It was administered prior to knowledge of the diagnosis (quasi-prospective design, because the disease may be present). Women with breast cancer had substancially higher scores than healthy and benign control groups in the two scales (p<.01). However, another variables has been found related to the variability of these scales (age, education level, and maternity). Thise findings are to be interpreted with caution because more controled research is need to determine de role of the psychosocial characteristics in the breast cancer onset.