Common warts caused by the human papillomavirus (HPV) are considered to be the most common infectious skin disease. No individual treatment for common warts is effective as monotherapy in eradicating the lesions. The aim of this study is to evaluate the clinical efficacy of a 35% and an 80% trichloroacetic acid (TCA) solution in the treatment of the common wart. In this single-blinded clinical trial, 62 eligible patients with common warts referred to the dermatology clinic of Ghaem Hospital in Mashhad, Iran. Patients were randomly divided into two groups, each treated with a TCA solution (group A, TCA 80%; group B, TCA 35%) once per week until complete clearance of the lesions or for a maximum duration of six weeks. Seven patients were excluded from the final analysis (one patient in group A and six patients in group B) for various reasons, including irregular follow-up, using physical tools such as razor blades to remove the lesion, and failure to complete treatment; and 55 patients were included in the final analysis. Improvement to treatment responses was classified as: no change (no changes in the number of warts), mild (clearing of less than 25% of warts), moderate (clearing of 25% to 75% of warts), and good (clearing of more than 75% of warts). At the end of follow-up, the clinical improvement of group A (n=30) was: 10 patients (33.3%) with a mild response, 6 patients (20%) with a moderate response, and 14 patients (46.7%) with a good response. In group B (n=25), 16 patients (64%) showed a mild response, 6 patients (24%) a moderate response, and 3 patients (12%) a good response. There was a statistically significant difference in improvement between the two treatment groups (P=.017). Improvement was greater with a higher concentration of TCA solution. This study showed that a different concentration of TCA solution was an effective form of treatment for common warts. Trichloroacetic acid 80% is more effective, but this solution must be used only with careful consideration by a physician.