Subclinical extension (SCE) of basal cell carcinomas (BCCs) may be responsible for incomplete resection of the tumor. The aggressive histological patterns (micronodular, infiltrative, and morpheaform) have greater tendencies toward invading surrounding tissues in an irregular pattern.To determine the SCE of small facial aggressive BCCs excised using Mohs micrographic surgery (MMS).An observational case series study. Data of patients with facial BCCs with aggressive histological patterns, less than or equal to 6 mm in diameter in high risk site (H zone), and 10 mm in intermediate risk site (M zone), treated with MMS between January 2008 and December 2016, were included.This study included 306 histologically confirmed lesions retrieved from 1,196 clinical records reviewed. Median size of tumors was 5.7 mm (interquartile range: 5-6 mm). Resection of the tumors using 2, 3, and 4 mm margins achieves complete excision of the lesion including the subclinical extension area in 73.9%, 94.4%, and 99% of cases, respectively.The present study demonstrated that a 4-mm resection margin was enough to eradicate the lesion completely in 99% of cases of primary small facial BCCs with aggressive histological patterns.