Aims Differentiated or HPV‐independent vulvar intraepithelial neoplasia (dVIN) can progress rapidly to invasive cancer and accurate pathological diagnosis is essential to facilitate appropriate interventions. Histological similarities of dVIN with non‐neoplastic lesions, however, often make the diagnosis less reproducible. We investigated among a diverse group of pathologists whether the diagnostic agreement improves with the use of p53 immunohistochemistry (IHC) interpreted using the pattern‐based schema. Methods and results Fifty haematoxylin–eosin (HE) stained archival slides (30 dVIN and 20 non‐dysplastic vulvar lesions) were selected and p53‐IHC was performed. Twenty‐four board‐certified pathologists from eight countries first assessed the HE slides alone, and after a washout period, re‐evaluated them alongside the p53‐IHC slides. During both rounds, slides were diagnosed as dVIN, favour dVIN, favour no‐VIN or no‐VIN. p53‐IHC was scored as wild‐type or mutant (diffuse, basal, cytoplasmic or null). Kappa ( κ ) statistics and McNemar's test were used for statistical analyses. Overall diagnostic agreement for dVIN saw a significant increase in the Kappa value ( κ = 0.6 vs. κ = 0.4, P = 0.002) when HE and p53‐IHC slides were assessed together compared with histology assessment alone, although the level of agreement remained moderate. For p53‐IHC assessment, overall agreement was substantial ( κ = 0.7). Diagnoses changing from no‐VIN/favour no‐VIN to dVIN correlated significantly with the identification of a p53‐mutant pattern ( P < 0.001). Conclusions Our findings indicate that p53‐IHC is a robust ancillary tool that can be reproducibly interpreted by pathologists with varying experience levels and supports the routine use of p53‐IHC in cases where dVIN is considered in the differential diagnosis.