In order to obtain information concerning the incidence of the various types of cancer in Iran, 40,690 identified cancer cases diagnosed in different histopathology laboratories in Tehran were studied. Skin cancer is the commonest form; 23% of all cases. The male/female ratio is a little more than 2:1. Cancer of the cervix uteri is the commonest form of cancer among women (19% of total cancer cases in women) and occupies the second place in the overall rating (8.60%). This also occurs predominantly in patients of the lower social classes. Primary cancer of the lymph nodes is very widespread in Iran. The general statistics show that primary malignant tumors of the lymph nodes comprise 8% of all cancer cases. Cancer of the esophagus occupies fourth place in the general statistics accounting for 7.5% of the total cases surveyed. Cancer of the breast (5%) occupies fifth place in the overall rating. Very few male patients have been diagnosed; the sex ratio being 1:28. Investigations show that breast cancer predominates among the higher social classes. Cancer of the respiratory tract is also common in Iran. From the total of 40,690 cases of cancer, 5.90% suffered from malignant tumors of these organs (3.30% cancer of larynx and 2.60% cancer of bronchus and lung). The incidence of malignant tumors of the prostate is very low and only 0.33% of all male cancer cases observed in Iran are localized in this organ.