Cancer is the third leading cause of death in Iranian population. Descriptive epidemiology provides a better understanding of the etiology of cancer and the development strategies. The objective of this study was to collect analysis of data and discuss certain epidemiologic features of neoplasm using data from hospital. Records of 14,540 patients diagnosed for cancer during the time period 1973-2003, who were referred to the department of radiation oncology were studied. The tumors were coded and classified according to the International Classification of Diseases 10th revision and ICD-O. SPSS version 10 was used for statistical analysis. In this study the frequency distribution of cancer patients were computed by age of diagnosis, gender, and anatomical sites. There were 8,178 male patients (56%) and 6,365 females (44%) with a male female ratio of 1.29. Mean age was 44.5?21.6 with a median of 47 years. The mean age of diagnosis for females (43.8.?.19.7) was significantly lower than that of males (45.0?23.1) (P<0.05). The ten most frequent cancer sites among patients were breast (13.6%), brain &CNS (13.6%), skin(13.5%), haemapoitic system(9.7%), lymphoid (7.1%), esophagus (7.1%), colon & rectum (4%), male genital organs (1.3%), bladder (1.3%), lung (1.2%), and stomach (1%). These accounted for 81% of all cases. It was found that 41% of women's cancers were in the breast, female genital organs compared to 7.3%in male genital organs and breast. All tumors except the breast, female genital organs, thyroid, gallbladder and kidney cancers, were more frequent in males compared to women. The frequency of patients with cancers increased with age in both sexes. Overall 53% of cases were between 40-63 years of age. For those aged 54 and below the male to female ratio was 0.99, while after this age the ratio rose to 1.61. About 16.6% of tumors occurred in children aged 15 years or younger. More than four fifths (81%) of patients with cancer of haematopoeitic system were under age of 15 years. In conclusion, the results of this study present an important epidemiological understanding of patients with tumors. It emphasizes that gender plays an important role in the frequency of primary tumors, and how much the sex ratio varies with some types of tumors. We also noted that certain tumor types show a prediction for certain decades of life in our series.