ObjectiveTo quantify the risk of residual invasion when cervical conization reveals microinvasive squamous carcinoma and to determine whether any factors affect this risk.MethodsWe reviewed the charts and histopathology slides of 87 women who underwent a conization that contained microinvasive squamous carcinoma, followed by either a repeat conization or hysterectomy. Depth of invasion, number of invasive foci, and status of the internal margin and post-conization endocervical curettage (ECC) were assessed. The findings were correlated with the presence of residual invasion.ResultsSignificant predictors of residual invasion included status of the internal margin (residual invasion present in 22% of women with an involved margin versus 3% with a negative margin;P<.03) and the combined status of the internal margin and post-conization ECC (residual invasion in 4% of patients if both negative, 13% if one positive, and 33% if both positive;P<.015). Depth of invasion and number of invasive foci in the conization specimen were not significant. The power of this study to detect a 25% difference in the risk of residual invasion was 73% for depth of invasion and 75% for number of invasive foci.ConclusionWomen with microinvasive squamous carcinoma in a conization specimen in which both the internal conization margin and post-conization ECC are negative have a low risk of residual invasion and are candidates for follow-up or simple hysterectomy. If either the internal margin or the post-conization ECC contains dysplasia or carcinoma, the risk of residual invasion is high and warrants repeat conization before definitive treatment planning.