Cancer is becoming an increasingly important cause of premature mortality in developing countries as their populations expand and their lifestyle becomes westernized. The aim of this study was to determine the frequency distribution of various neoplasms among Iranian inpatients, their demographic status and length of stay involved in hospitals during 2000-2002. Records of 17447 inpatients who were hospitalized with malignant tumors in Iranian public hospitals during 2000-2002 were studied. The neoplasms had been coded and classified according to International Classification of Diseases, 10th Revision (ICD-10). The frequency distribution of cancer patients was evaluated by age, sex, place of residence and the length of stay at hospital. There were 9470 male patients (54.3%) and 7977 females (45.7%). The mean ± sd age was 51.2±20.6 with a median of 55 years. The average for females (49.4±19.2 yrs) was significantly lower than that for males (52.8±21.7 yrs) (p<0.001). The five most common cancer sites were the digestive organs (27.6%) followed by lymphoid and haematopoitic tissues (21.4%), breast (10.2%), respiratory and intrathoracic organs (8.8%) and skin (6%). These accounted for 74% of all malignancies. Some 31% of women’s cancers were found in breast or genital organs compared to only 7.6% for males. The male/female ratio was 1.19 with the highest being 2.85 for respiratory organs and the lowest being 0.04 for breast. Mean age of male patients with cancer of the digestive organs, respiratory and intrathoracic organs and skin was significantly lower than that of females (p<0.001). The median length of stay of patients in hospitals each time they were admitted was 6 days. Of the cancer patients, 77.7% lived in urban areas which include only 64.5% of the population. Rural patients with skin cancer accounted for 32.1%. In conclusion, the results of this study carry important implications for future health planning strategies and provide a baseline for further studies on the evaluation of malignancies in Iran.