Pouwer AFW, Bult P, Otte I, et al. - Fifty slides of vulvar squamous cell carcinoma (SCC) with a depth of invasion approximately 1 mm were selected, digitally scanned and independently evaluated by the researchers in order to evaluate interobserver agreement for classifying the depth of invasion via both methods and to recognize pitfalls. Using both the conventional and alternative methods in each slide, the depth of invasion was calculated and classified into ≤ 1 and > 1 mm. For the multi-rater agreement, the percentage of agreement and Light’s kappa were measured, and 95% confidence intervals were calculated with bootstrapping. Modest agreement using the conventional method was found. Among the participating pathologist, the percentage of agreements obtained via the conventional method was 85.0% vs 89.4% via the alternative method. Disagreement concerning which invasive nest was deepest, identification of invasive growth and where it began, curved surface, carcinoma located on the edge of the tissue block, ulceration and various measurement methods were six pitfalls that were recognized. Hence, in discovering the depth of invasion in vulvar SCC, pathologists reached an only moderate agreement, without a significant variation among the two measurement methods.