This report presents the results of a study of direct treatment costs of AIDS in Mexico, carried out in five public hospitals, four social security hospitals and one private hospital. The study included: a retrospective phase, a prospective phase and a longitudinal followup. The study found that the average AIDS patient has a total of two hospital admissions per year, with an average stay of 20 days per admission, and an annual cost of almost $4,043 US. The hospital admission costs per patient ranged between $1,430 US and $7,350 US with an average cost of $2,565 US. The outpatient's treatment costs per year were of $300 US. The patient's expenses at their homes were $1,100 US. We conclude that treatment costs for AIDS patients, excluding use of AZT, are higher than the treatment costs of comparable diseases. The greatest cost is that for inpatient care; thus, we recommend improving outpatient care services in order to provide more comprehensive care to patients and their families.