The true risk population for uterine and ovary cancer have been studied, according to the prevalence of histerectomy and oophorectomy in the Trieste area female population. The calculation of the females at risk for these tumors permits to recalculate the incidence rates that are usually underestimated. This adjustment increases the rates in all genital tract tumors from 14% to 18%, but does not modify the relative frequency per age groups or the incidence in the temporal trends. An exception is represented from the uterine corpus cancer in which the correction of the population modifies the temporal trend for the age group over 60 years. The incidences tend in fact to increase significantly more after the adjustment.