BACKGROUND: This study was conducted in order to examine the duration of lupus anticoagulant (LA) presence in serum after it was first detected in children in association with infection. In addition, the effect of LA on coagulation time was evaluated. METHODS: We included 14 children who had an accompanying high titer of LA and prolonged prothrombin time (PT) or activated partial thromboplastin time (aPTT). The titer of LA and PT/aPTT were examined until LA titer normalized serially after an interval of approximately 10 days. RESULTS: None of the subjects showed any evidence of bleeding or thrombosis during conduct of the study. LA titer had normalized in none of the subjects within approximately 10 days later, and only 28.6% within 20 days later. However, LA titer had normalized in 85.7% of subjects within approximately 30 days, and all subjects showed the normal range of LA titer at 40 days from the first examination. LA titer had a statistically significantly effect on the PT and aPTT (P<0.05, P<0.01, respectively). CONCLUSION: The prolongation of PT or aPTT observed in children with high titer of LA after infectious diseases was not related to any bleeding or thrombotic problem. The elevated titer of LA and prolonged aPTT normalized within approximately 40 days. However, the number of subjects in this study was too small; therefore, conduct of a larger cohort study will be required in order to clarify that elevated LA is related to clinical problems.