OBJECTIVE To assess patterns of histopathological outcomes reported in microinvasive oral squamous cell carcinoma (OSCCmi) cases. STUDY DESIGN An online search in major databases was performed without period restriction, in which 2,024 publications in English, Spanish, and Portuguese were obtained. After screening and eligibility, 4 studies were selected. The risk of bias was assessed using Joanna Briggs Institute Critical Appraisal Checklist. A descriptive synthesis was conducted. RESULTS All 4 publications were retrospective, reporting a total of 116 OSCCmi patients, with a male predominance (1.6:1) and a mean age of 55.9 years. The main parameters considered for microinvasion were tumor thickness (TT) (range 4-10mm) and depth of invasion (DOI) (range 0.02-5mm). Definition, cut-off values, and assessment of microscopic features were not standardized. Other relevant measures, such as perineural or lymphovascular invasion and pattern of invasive front were barely described, and cytological/architectural characteristics were not considered. CONCLUSION TT and DOI are currently the primary histopathological criteria used to define OSCCmi. Nonetheless, the outcomes of this systematic review showed the absence of standardized quantitative parameters to render the diagnosis of incipient OSCC. Therefore, additional studies aiming to standardize histopathological outcomes to report OSCCmi are of utmost importance. To assess patterns of histopathological outcomes reported in microinvasive oral squamous cell carcinoma (OSCCmi) cases. An online search in major databases was performed without period restriction, in which 2,024 publications in English, Spanish, and Portuguese were obtained. After screening and eligibility, 4 studies were selected. The risk of bias was assessed using Joanna Briggs Institute Critical Appraisal Checklist. A descriptive synthesis was conducted. All 4 publications were retrospective, reporting a total of 116 OSCCmi patients, with a male predominance (1.6:1) and a mean age of 55.9 years. The main parameters considered for microinvasion were tumor thickness (TT) (range 4-10mm) and depth of invasion (DOI) (range 0.02-5mm). Definition, cut-off values, and assessment of microscopic features were not standardized. Other relevant measures, such as perineural or lymphovascular invasion and pattern of invasive front were barely described, and cytological/architectural characteristics were not considered. TT and DOI are currently the primary histopathological criteria used to define OSCCmi. Nonetheless, the outcomes of this systematic review showed the absence of standardized quantitative parameters to render the diagnosis of incipient OSCC. Therefore, additional studies aiming to standardize histopathological outcomes to report OSCCmi are of utmost importance.