We developed an algorithm to select incident cases of lymphatic and haematopoietic system in children, in order to create a timely and accurate database of incident cases to answer the needs of cluster analysis. This group of cancers is by far the most frequent in the paediatric age. The procedure has been applied to identify incident cases in children aged 0-14 years, resident in Rome (Central Italy), and diagnosed between 2000 and 2011. The algorithm links hospital discharge records (SDO), the hospital registry of the Italian Association of paediatric haematology and oncology (AIEOP), and the Population Registry. We identified 391 cases of cancers of lymphatic and haematopoietic system; among them, the most frequent pathology is the lymphoid leukaemia, which represents 52% of total cases, followed by non-Hodgkin lymphoma (21% of total cases). Results correspond to data from literature and to the estimates from the Italian Association of cancer registries (AIRTUM), giving value to the used procedure.