OBJECTIVE: to evaluate the structure and the admission process for acute pyelonephritis (APN) and to qualify the different alternatives. To calculate costs associated to any therapeutic, antibiotic or not, and diagnostic, laboratory or instrumental pathway and to notice their behaviours. To estimate the amount of this share of hospital costs on the global and to compare them to reimbursements. METHODS: A retrospective analysis was made of all admissions with a diagnosis of APN in the Nephrology Department of Ravenna Local Health Unit between 1/1/1985 and 31/12/1998 as well as an assessment of therapeutic costs and diagnostic charges (defined clinical costs) and reimbursements in accordance with the DRG. Data were collected thanks to a specific software purposely developed. An economic analysis was conducted relating costs to length of stay and to risk factors. RESULTS: The number of patients admitted was determined (69 females and 8 males, aged 35.4+16.8). Average duration of hospitalisation: 11.2+3.2 days. Total clinical costs: ITL. 81,389,282, 69.3% due to tests and 30,7 to drugs (mean cost per patient: ITL. 1,190,015 for DRG 320, ITL. 1,049,115 for DRG 321 and ITL. 832,540 for DRG 322, respectively: 22.9%, 31.7%, and 24.6% of the reimbursement). Clinical costs peaked in first days, caused by diagnostic ones, then tailed off gradually. The 62.7% of tests was performed within the third day. The mean cost of this period next to admission was the 37.9% of the total mean cost per patient. DISCUSSION: the analytical knowledge of diagnostic and therapeutics pathways premises to find out the clinical algorithms and their costs and to analyse the relationship between resources and results. The clinical costs for the APN patient in hospital account for a considerable share of the DRG reimbursement which may therefore be “overbalanced” by the hotel costs (not clinical).