Today, chronic diseases have increased importance. Cancer, for which 10 million new cases are diagnosed around the world each year, is in the lead of such diseases. This study included military personnel with cancer who applied to the Department of Medical Oncology, Gülhane Military Medical Academy, in the period between 1998 and 2003, and it aims to describe some sociodemographic and diagnostic characteristics of the patients. The total number of cases was 938, which included both active duty and retired military personnel with diagnoses of cancer who were given medical care between 1998 and 2003 in the Department of Medical Oncology. For the study group, the five most common diagnoses were lung cancer, colorectal cancer, testicular cancer, non-Hodgkin's lymphoma, and Hodgkin's disease. Although the first three diagnoses among officers were lung cancer, testicular cancer, and Hodgkin's disease, those among retired officers were colorectal cancer, lung cancer, and prostate cancer. Among noncommissioned officers, the first three diagnoses were colorectal cancer, testicular cancer, and Hodgkin's disease for active duty patients and lung cancer, colorectal cancer, and gastric cancer for retired patients. In the group of privates, testicular cancer, Hodgkin's disease, and non-Hodgkin's lymphoma were the first three diagnoses. When we consider the characteristics of cancers, such as high costs of treatment, loss of manpower, and high mortality rates, prevention of cancers and early diagnosis are very important. Because the frequent types of cancers differed for groups according to age and occupation, those characteristics should be considered when cancer screening programs are being developed for the Armed Forces.