Over utilization of anti-infective agents is a worldwide problem. The Anatomical Therapeutic Chemical (ATC) classification/DDD system is adopted by the world health organization (WHO) for drug utilization research to compare the pattern of drug usage at international level. This is the first study in Palestine that uses this methodology. The study was carried out for 30 consecutive days (23/10/2005-23/11/2005) in the internal wards at Al-Watani governmental hospital in Nablus-Palestine. Data collected included, age sex, diagnosis, anti-infective agents prescribed, dosage regimen and number of doses of antibiotic administered. Data were analyzed using SPSS version 12. DDD/100 bed-days were calculated for the anti-infective agents using the international formula.During the study period, 442 patients were admitted to the internal wards. The patients were 193 females (43.7%) and 249 males (56.3%). Among these patients, 191 (43.2%) were prescribed anti-infective agents. Cefuroxime, ceftriaxone, and metronidazole were the most frequently prescribed with the percentages of 27.8%, 6.1% and 5.7% respectively. The total amount of anti-infective agents prescribed was 38.99 DDD/100 bed days. The DDD/patient/day was 0.4 compared to 1 DDD/patient/day as the optimum. The results of this study reflect a deviation from the optimum use of anti-infective agents. Optimizing anti-infective therapy is necessary.