Background: Mohs micrographic surgery (MMS) is believed to be a highly effective treatment of squamous cell carcinoma (SCC) of the lip. Objective: The goals of our study were to determine the long-term (5-year) outcome of patients treated with MMS for SCC of the lip and to identify factors associated with tumor recurrence. Methods: Clinical and histopathologic data from 50 consecutive cases of SCC of the lip treated with MMS were retrospectively reviewed. Results: There were no tumor-related deaths or metastases. Forty-six patients (92%) remained free of disease. Four patients (8%) were diagnosed with SCC at the surgical site after MMS. Recurrent lesions tended to be superficial and occurred in the setting of severe actinic cheilitis. The average time to diagnosis after MMS was 2.5 years. All patients with recurrent disease were treated with further MMS and had successful results. No recurrences were seen among patients who received adjuvant treatment for actinic cheilitis with the carbon dioxide (CO₂) laser, had clinical lesions 1 cm or less in diameter, or had post-MMS defects 2 cm or less in diameter. Conclusion: MMS is highly effective for treating both primary and recurrent SCC of the lip. Treatment of coexisting actinic cheilitis may lower the risk for local recurrence after MMS.(J Am Acad Dermatol 1998;38:960-6.)