Patients with atopic dermatitis (AD) are susceptible to cutaneous bacterial infection. When such patients develop infection, some have extensive impetiginized dermatitis with high fever. To clarify the risk factors for severe impetiginized AD and its microbiological features, we reviewed clinical and microbiological data of 14 patients with impetiginized AD who were admitted to our hospital between the years 1999 and 2006. All patients had poorly controlled AD with eczematous lesions on the extensive body surface. The mean age was 28.2 years (range 18-35). Cultures of the lesional skin yielded both Streptococcus pyogenes and Staphylococcus aureus in 12 patients. S. pyogenes alone was isolated in two cases. These observations suggest that poorly controlled AD in adults is a risk factor for severe impetiginized AD and that S. pyogenes might play an important role in the development of severe clinical symptoms.