Background: Diphenylcyclopropenone (DPCP) immunotherapy has been shown to be efficacious for the treatment ofwarts, especially periungual warts for which destructive techniques are limited. However, factors affecting the duration of treatment of periungual warts have not been studied. Objectives: This study was designed to evaluate the factors contributing to the treatment duration of DPCP immunotherapy for the treatment of periungual warts. Methods: A total of 61 patients with periungual warts who were completely cured with DPCP immunotherapy were included in this study. Age, sex, disease duration,location, number of warts, diameter of the largest wart, application number for sensitization and two types of sensitization reactions, erythema and blister index (EBI), and pruritus index (PI) were evaluated. We analyzed the correlations of these variables with the treatment duration. Results: Of the nine variables, application number for sensitization (regression coefficient = 3.251 and 2.428, respectively) and EBI (regression coefficient = -9.950 and -9.694, respectively) were independent factors significantly affecting both the total duration of treatment and the duration of treatment after sensitization (P < 0.05, respectively). Conclusion: A shorter sensitization period and more severe EBI of the sensitization reaction contribute to a shorter time required for a complete cure in the treatment of periungual warts with DPCP immunotherapy.