Cellulitis is a common problem presenting to the emergency department (ED). This study examines the epidemiology of cellulitis in 5 Canadian urban EDs and determines the practice variation in this management among sites. From computerized provincial ED diagnosis information, 10% of cellulitis charts from April 1, 1997 to March 31, 1998 were randomly selected for review. All 5 EDs in one urban region were sampled; physicians were unaware of the study when seeing patients. A standardized audit form was used to collect information pertaining to visits for the incident infection case. Cases were excluded if simple cellulitis was not the primary diagnosis or if procedures such as incision and drainage were initially required. A total of 416 adult charts were retrospectively identified. The mean age was 46 years and 61% were men; 38% had seen another physician before the ED presentation. Cellulitis was most commonly located in the upper (41%) and lower (48%) extremities. Most cases were treated with intravenous cefazolin (58%; range among sites: 49%-66%); however, over 25 different antibiotics and doses were initially prescribed. Each case required a median of 4 (interquartile range [IQR]: 1, 9) ED visits. Some patients (14%) received an increase in dose (3%) or a change in antibiotic regimen (11%) during their treatment. Few patients (3%) required a second change in regimen. Specialist consultations were obtained in only 6% of patients and hospitalization was rare (7%). The most common discharge prescription was oral cephalexin (62%); however; many different regimens were prescribed. Cellulitis is a common ED problem which consumes considerable resources to treat. Considerable practice variation exists with respect to in-ED and post-ED management. These results suggest the need for the development of practice guidelines for the treatment of this common ED problem.