The sentinel lymph node (SLN) procedure is used in our institute in the setting of an observational multicenter study investigating the reliability of the sentinel node procedure in vulvar carcinoma (GROINSS-V: The Groningen International Study on Sentinel Nodes in Vulvar Cancer). One of our patients had a groin recurrence where the SLN had been reported as negative. After reviewing this SLN, it contained several anucleate, keratin-positive structures on immunohistochemistry, and in the same area on hematoxylin and eosin coloring, one single cell with a nucleus interpreted as a tumor cell. Our objective was to assess how frequently these anucleate structures occur and whether such nodes should be regarded as positive. The sentinel nodes from 32 patients with early-stage vulvar squamous cell carcinoma were reviewed. Seventy-seven SLN's were identified. In ten patients, the SLN was positive and a bilateral inguinofemoral lymph node dissection was subsequently performed. In two of these ten patients, both with a macrometastasis on SLN, further metastatic disease was present in the dissection specimen. Anucleate keratin-positive structures were seen on immunohistochemistry in 14 SLN's (18%), usually along with metastasis or single tumor cells, but in five nodes this was the only abnormality (mean follow-up period of 26.28 months). Anucleate keratin-positive structures are a common finding in immunohistochemical examination of SLN's. Our findings suggest that they are of no clinical significance and the SLN should be regarded as negative. When an atypical cell with a nucleus is present, the SLN should be classified as positive and further management should be accordingly.