Background: There is evidence to postulate that undernotification is the reason for the great decrease in the reported incidence of hydatidosis in Chile. Aim: To develop and propose a method to assess the notification of transmissible diseases, based on observed lethality and hospital discharges. Material ann methods: Human hydatidosis in the period 1985-1994 was used as a model to develop the method. Official reports and mortality were analyzed first, determining the first lethality rate. A second lethality rate was calculated based on hospital discharges and a third, based oil all Chilean surgical series published iia the last two decades. Adjusting official notification of lethality to the true lethality according to surgical series, the number of unreported cases was calculated and the true incidence of hydatidosis was calculated summing these cases to the official notification. Results: According to this method the real rates of human hydatidosis in the period 1985-1994, would fluctuate between 6.5 and 11.4 per 100,000. This figure is four times higher than the official notification in the analysed period. Conclusions: The correction of under notification based oil hospital discharges, with or without correction for repeated hospital admissions, or real mortality of surgical series gave similar results, suggesting that both methods are correct.