The influence of war circumstances on tumor morphological characteristics in patients with breast cancer has not been studied up to now. The aim of this study is to investigate if war circumstances have influenced breast cancer incidence. The study covered both the patients in which during a period of observation a breast cancer was diagnosed as well as those who died of the same disease in the same period. Three sources of data were used: 1) The archives of the Oncology and Radiotherapy Center of the University Hospital "Split" (UHS): hospital data of 768 patients were reviewed. The war sample consisted of 380 patients aged 59.4+/-12.1 (31 to 86) (including 5 males), whereas the pre-war sample was made up of 388 patients aged 58.4+/-12.7 (19 to 88) (including 3 males); 2) Register of death of the Pathology Department of UHS with 162 analyzed persons whose death was caused by breast cancer in the six-year period between 1988 and 1993. The list of 162 dead patients included 79 people who died from breast cancer diagnosed in that period (1988-1993) and another 83 people that had been diagnosed before that period; 3) The biopsy register of the Pathology Department of UHS with 851 breast biopsies performed between 1988 and 1993. Breast cancer is predominantly a female illness (99.1%). The war circumstances influenced the of T, N and M rate. The rate of N2, N3, Ml were conspicuously higher in the war period. There were significantly more malignant histological diagnoses found in new patients and also significantly more patients died due to breast cancer. Stress and other war circumstances undoubtedly have a negative impact on the numerous markers of breast cancer which we have proved in this study.