To make and validate a data base that allows to collect information about clinical characteristics and use of health care services by HIV-infected patients. An additional purpose is to obtain some data about costs of health care services utilization. We have designed an informatic data base that includes: demographic data, clinical data and health care services utilization during the follow up. One hundred and nine patients were selected from 5 different hospitals in Spain and they were followed for 6 months (from January to June 1997). Analytic accounting of one hospital and official tariffs were used to calculate costs of the health care services. The informatic data base designed is useful and appropriate to collect the information of these patients. The annual average cost is 2.5 millions dollars, ranging from 1 million dollars for asymptomatic patients to 3.8 millions for AIDS patients. The comparison of our results with previous studies shows an increased cost of asymptomatic patients. These results give a preliminary information about health care services utilization by HIV-infected patients and confirm the possibility of using the designed instrument in the future. Since HIV-infection presents an uncertain evolution and a variable prognosis, to implant a tracking system is a necessary requirement in order to obtain a fast and accurate information system about the evolution of clinical variables and their economic repercussions.