BACKGROUND. Information on frequency of consultation and presented morbidity among patients with chronic disease is relevant to the management of these patients in view of the increasing prevalence of chronic diseases. AIM. This study set out to examine consultation rates and incidence of intercurrent morbidity in general practice in cohorts of patients with five common chronic diseases: hypertension, chronic ischaemic heart disease, diabetes mellitus, chronic respiratory disease and osteoarthritis. METHOD. In seven practices with 15 general practitioners the records of all patients were screened for inclusion in the study. The data used for analysis were from 962 patients, whose diagnoses were made in agreement with diagnostic criteria, who were not under specialist care, and who were followed up for 21 months. A distinction was made between patients with one, or two or more of the five chronic diseases studied. For the single disease subgroups of patients with hypertension or diabetes two reference groups of people without a chronic disease, standardized for age and sex, were identified from the population in the same practices. RESULTS. Consultation rates were higher for patients with comorbidity than for patients with a single disease. Intercurrent diseases were presented more frequently to the general practitioner by patients with comorbidity than by patients with a single disease. Most intercurrent morbidity consisted of acute common diseases such as myalgia, upper respiratory tract infection and urinary tract infection. Patients with only hypertension or only diabetes had higher consultation rates than the corresponding reference group but did not have higher total incidence rates of intercurrent morbidity. CONCLUSION. Patients with chronic disease consult their general practitioner frequently, and patients with more than one chronic disease consult even more frequently. The general practitioner has to deal with chronic disease and intercurrent acute disease in a single patient.