Objective: This article is to calculate corrected Iran cancer incidence by a novel method to compensateunder-ascertainment of cancer cases in the very elderly (aged 65+). Study Design and Setting: Corrected agespecificrate for a certain cancer in age group 65+ was calculated from the age-specific rate of that cancer in agegroup 55-64 multiplied by the corresponding coefficient from reference cancer registry (sex- and age-specificcoefficients from Finnish Cancer Registry, a nation-wide registry with high validity of data). All cancer datawere obtained from GLOBOCAN 2002. Results: The crude rate (and number of new cases) for “All sites excludingskin” was 13.6% (men 18.7%; women 8.1%) under-estimated. The under-enumeration was 18.9% for the agestandardizedrate (men 25.4%; women 11.8%). This means there were 58,000 new cancer cases (about 7,000more than original) in 2002. Corrected incidence for the year 2050 was 26.1% higher (men 32.8%; women17.3%) than the original estimate (49,000 more). Depending on cancer site and sex, percentage under-estimationvaried remarkably. Conclusion: After correction, the estimates of number of new cases and incidence rates ofIran increase substantially. Without correction, cancer occurrence measures can be remarkably under-estimatedwhich may lead to inadequate resource allocation for control measures.