The outcome of Helicobacter pylori infection was analyzed in 114 dyspeptic patients treated with triple-drug therapy including clarithromycin. Clarithromycin resistance (in 20.2% of our isolates) was mainly caused by an A2142G mutation in the 23S rRNA gene of H. pylori. H. pylori eradication was obtained in all patients with clarithromycin-susceptible isolates but not in any patients with clarithromycin-resistant isolates (P = 0.0001). Therefore, it would be useful to conduct H. pylori antimicrobial susceptibility testing of the first gastric biopsy culture before choosing the first three drugs for therapy of infected patients.