BMC Cancer 2005, 5:33 http://www.biomedcentral.com/1471-2407/5/33 Salvadoran group of 0–11 year olds were 34.2, 7.1, 0.6, 0.2, and 43.2 per million children for ALL, AML, CML, UL, and total leukemias, respectively. Conclusion: Reported AIRs for each age group in El Salvador were similar to those from other American countries. The AAIR of ALL in Mexico City is one of the highest reported for North America. Background Leukemias are the most frequent type of cancer in child- hood [1], the incidence of which varies depending on the area of the world where they are studied [2]. An elevated frequency of acute leukemias has been reported in popu- lations of Hispanic origin [3-5]. For example, in Costa Rica, the highest incidence rate in the world for acute leukemias has been reported: 56 per million of children under the age of 15 years [5]. In California and Texas, two states of the U.S. which have a Hispanic component pre- dominately of Mexican origin [3], the incidence rates for ALL and for AL in general have been found to be greater than those previously reported for Mexico City [6-8]. However, because the studies carried out in Mexico City have been retrospective, it is possible that a under-register of the infirmity may have existed in Mexico City. In Flor- ida, the state with the highest predominance of Hispanics of Caribbean and Central American origin, the incidence rate of ALL was higher than that reported for the Cauca- sian population and similarly elevated to that reported for Costa Rica. For the Central American country of El Salva- dor, there is no prior information on the incidence of acute leukemias. In developing countries, there are few data on the fre- quency of leukemias during childhood [5,9] because these countries have not had the infrastructure required to keep reliable records. Some international studies have produced information from some developing countries, particularly in Latin America [10]; however, this informa- tion has certain constraints with respect to its validity and coverage in representing the populations [11-15] Of the studies carried out in Mexico City, an important increase in the incidence of ALL, but not of AML, has been reported. In 1991, an incidence of 22.2 per million of chil- dren under 15 years of age was reported [6]. From the data from the Instituto Mexicano del Seguro Social, the Medi- cal Center having the greatest coverage of the population in the whole of the country, an incidence rate was reported of 29.1 per million of children under 15 years of age who were residents of Mexico City and who had the right to receive attention from this Institution [7]. Given the retrospective nature of these studies, it is possible that there was underestimation of the incidence rate of ALL. On the other hand, when taken into account that, in the different states in the U.S. which have a high component of Hispanics of Mexican origin, the incidence rate of acute leukemias is the highest in the world, one may consider it important to perform a prospective population-based study in Mexico City that would determine if Mexican children, residing in this City, had an incidence rate simi- lar to those reported for Texas and California [3]. Prospective records of those children treated for leukemia was initiated in El Salvador in 1994 and in Mexico City in 1996 [16,17]. In Mexico City, the record was kept in the hospitals of the Instituto Mexicano del Seguro Social (IMSS), an institution that attends about 50% of the pop- ulation inhabiting Mexico City [7]. Because the IMSS keeps a register of the population that has a right to receive medical attention at its facilities, the base popula- tion is known and it is feasible to obtain the incidence rate for the population under 15 years of age. In El Salvador, because the record was kept by the Hospital Nacional de Niños "Benjamín Bloom" (BB), the only center in the country which attends all children, younger than 12 years with oncologic disease, data on the population base which was necessary for calculating the incidence rate was available. Treatment of children with leukemia is com- pletely free of charge both in El Salvador and at the IMSS in Mexico City, thus allowing a greater coverage for chil- dren with this disease [16,17]. This work presents the incidence of leukemia in children younger than 12 years, because this is the age range admit- ted in the BB and data for children younger than 15 is used for Mexico City. In this report, for purposes of anal- ysis, the data from 1996–2000 were used, with 1996 being the first year of record keeping in Mexico City and 2000 being the most recent year for data reported from El Salvador. Methods Design Population-based data. Hospitals The Hospital Nacional de Niños "Benjamín Bloom" (BB), located in San Salvador, capital of El Salvador; is a tertiary care center and is the only hospital in that country that has a pediatric hematology-oncology service with pediatric hematology staff. Being the only domestic reference center for pediatric oncologic diseases, it is the only hospital to which children with presumed leukemia diagnosis are Page 2 of 9 (page number not for citation purposes)