The study in which we investigated some sociodemographic characteristics and diagnoses of 2667 patients who were followed with cancers of various systems and organs at Gülhane Military Medical Academy Medical Oncology Department between 1998-2003, is a descriptive study. The mean age of patients was 51.9 ± 16.8 (median=55). Of the patients, 56.8% were male, and 23.1% were under 40 years old (29.4% of male patients and 16.1% of female patients). According to status, family members of military personnel were the biggest group with 40.5%. According to frequencies of diagnoses; lung cancer, colorectal cancer, and gastric cancer for men and breast cancer, colorectal cancer, and gastric cancer for women were the first three diagnoses. While in group of under 40 year old men testicular tumors were the most frequent diagnosis, in other age groups of men, lung carcinoma was most frequent diagnosis. In women, breast cancer was the most frequent diagnosis in all age groups. When we consider the characteristics of cancers such as high cost of treatment, loss of manpower, and high mortality, prevention of cancers and early diagnosis are very important. Because the frequent types of cancers differ for groups of age and sex, while cancer screening programs are developed those characteristics should be considered.