Background: Fourty years of morbidity registration in general practice is a milestone urging to present an overview of outcomes. This paper provides insight into the infrastructure and methods of the oldest practice-based research network in the Netherlands and offers an overview of morbidity in a general practice population. Changes in morbidity and some striking trends in morbidity are presented. Methods:The CMR (Continuous Morbidity Registration) collects morbidity data in four practices, in and around Nijmegen, the Netherlands. The recording is anchored in the Dutch healthcare system, which is primary care based, and where every citizen is listed with a personal GP. Trends over the period 1985-2006 are presented as a three year moving average. As an indicator for 20-year prevalence trends we used the annual percentage change (APC). We restricted ourselves to morbidity, which is presented to the family physician on a frequent basis (overall prevalence rates <1.0/1000/year). Results: The age distribution of the CMR population is comparable to the general Dutch population. Overall incidence figures vary between 1500/ 1000 ptyrs (men) and 2000/1000 ptyrs (women). They are quite stable over the years, whereas overall prevalence figures are rising gradually to 1500/2500 ptyrs (men) and 2000/3500 ptyrs (women). Increase in prevalence rates for chronic conditions is diffuse and gradual with a few striking exceptions. Conclusion: For morbidity patterns, the CMR database serves as a mirror of general practice. Practice-based research networks are indispensable for the development and maintenance of general practice as an academic discipline.