The aims of this study are: to evaluate the prevalence of chronic diseases in the Brazilian population comparing data of 2008 with those of 2003; to estimate the impact of chronic conditions on the use of health services and on the restriction of daily activities and to measure the differentials in the prevalence of specific diseases according to educational strata and the affiliation to a private health plan. Data were obtained from PNAD 2008 and 2003. The analysis included estimations of crude and adjusted prevalence ratios, using svy commands from Stata 11 software. The prevalence of at least one disease was higher in: the elderly, women, low schooling level, black or indigenous people, urban residents, migrants and people living in the south region of Brazil. The most frequent diseases were: hypertension, back and spinal cord disorders, arthritis and depression. Between 2003 and 2008, an increase in the prevalence of diabetes, hypertension, cancer and cirrhosis was observed, and there was a reduction in chronic kidney failure and tuberculosis. All the diseases analyzed, with the exception of cancer and tendinitis/tenossinovitis, revealed a higher prevalence in low educational level strata. The greatest social inequalities were in chronic kidney failure, cirrhosis, tuberculosis and arthritis/rheumatism.