Eighty two patients with chronic urticaria and 17 patients with prurigo chronica multiformis were referred to our department from October 2004 to February 2007 and were tested for Helicobacter pylori antigen using the polyclonal H. pylori stool antigen test (enzyme-linked immunosorbent assay method). H. pylori antigen was detected in 25 (30.5%) of the 82 patients with chronic urticaria and in 10 (58.8%) of the 17 patients with prurigo chronica multiformis. Those findings were not significantly higher than the positive rate for H. pylori stool antigen in healthy age-matched controls. In patients positive for H. pylori antigen, seven of the 25 with chronic urticaria had complications of gastritis (six patients) or gastric ulcers (one patient). Three of the 10 patients with prurigo chronica multiformis had complications of gastritis (two patients) or gastric ulcers (one patient). We examined the therapeutic efficacy of antibacterial treatment for the 17 patients with chronic urticaria and the eight patients with prurigo chronica multiformis who were positive for H. pylori antigen and accepted the treatment based on informed consent. We evaluated the effectiveness of treatment by scoring the skin conditions and by using the Skindex-16, a measure of quality of life. The eradication therapy for H. pylori was more effective for treating prurigo chronica multiformis and the skin symptoms started to improve within 3–14 days after the therapy. However, that therapy was not always effective for treating chronic urticaria. We suggest that H. pylori may be an important pathogenetic factor, especially for prurigo chronica multiformis, and that eradication therapy should be considered to treat intractable cases.