Concerns have been expressed about the overuse of antibiotics in inpatient settings. We compared the pattern of antibiotic use in 2010 in a surgical unit of a university hospital in the Islamic Republic of Iran with similar data from 2006. Defined daily doses per 100 bed-days (DBD) were calculated. Overall use of antibiotics in our surgical unit increased significantly from a mean of 4.9 (SD 5.1) DBD in 2006 to 7.7 (SD 10.3) DBD in 2010. This increase was mainly due to increases in the use of antibiotics for treatment of infections; the prophylactic use of antibiotics did not show a significant increase. There was an increase in the consumption of ceftriaxone, imipenem, cefalotin, metronidazole and vancomycin, a decrease in the use of erythromycin and ceftazidime and no change in the use of ciprofloxacin and clindamycin. Ceftriaxone showed the greatest increase (5.1-fold) and erythromycin the sharpest decrease (8-fold) in use.