Follow-up studies on health have usually been based on ad hoc cohort studies in which detailed information is collected specifically for research purposes on a certain group of people. The increasing collection of routine health data provides an alternative method of gathering follow-up data. In this study, the feasibility of using routinely collected health-register data and data linkages to follow up children's health was investigated. Five nationwide registers, 18 regional registers of intellectually disabled children and school administration data in one county were found to be of use for our follow-up and were combined with the 1987 Finnish Medical Birth Register (n = 60,254 births). In the follow-up, 62 children were untraced (0.1%), 327 were stillborn (0.5%), 440 died after birth (0.7%) and 287 emigrated (0.5%) before the age of 7 years. The cumulative incidences for all diseases (8.9% of all children living in Finland at the age of 7 years), for diabetes (3.0/1000), for epilepsy (6.8/1000) and for asthma (34.2/1000) correspond to the estimates of other studies, but our estimate for intellectual disabilities (18.0/1000, of whom 18% were reported to have an IQ of 70 or less) seems to be an underestimate. Our data collection did not provide reliable information on institutionalised children or children taken into care. Data collection conducted by using health registers is a feasible method, and it saves both time and financial resources compared with cohort studies. Potential problems with data linkage studies are variation in the content of data and in data quality of different registers and data protection issues.