General practice is an important source of information on the occurrence and distribution of chronic disease in the population. In this study, the burden of chronic illness was expressed as different indices of prevalence. Data were provided by 42 general practitioners in 15 computerized practices, collaborating in the Registration Network Family Practices of the University of Limburg in the Netherlands. Morbidity data concerning the actual health status of 25,357 subjects, as recorded by their GPs, were classified following the International Classification of Primary Care using the diagnostic criteria of the International Classification of Health Problems in Primary Care-2-Defined. The most frequent single disease was asthma (3.5%), while locomotor problems represented the most prevalent category (8.3%). The overall prevalence of chronic disease was 29.4%, with a clear positive correlation with age and, to a lesser extent, with a lower educational level. The 'social prevalence' of chronic illness (including individuals related to chronically diseased patients via their households) could be measured in a subset of the database (n = 4577), and amounted to 56%. It is concluded that the role of the GP as a family doctor involved with chronic disease concerns the majority of the general population.