Despite approximately 4,400 unresectable U.S. cases annually, high-stage basal cell carcinoma (BCC) is ill-defined.Develop a tumor (T) staging system for BCC predicting metastasis/death and compare its performance to AJCC 8th edition (AJCC8) T staging.BWH T staging was developed from a previously published nested cohort of 488 primary BCCs. Tumors were staged via BWH and AJCC8 T staging systems and prediction of metastasis and/or death was compared.BWH and AJCC8 T staging systems both captured all metastases/deaths in high T stages (BWH T2; AJCC8 T3/T4). BWH T2 included 54% fewer cases ≥2cm compared to AJCC8 T3/T4. BWH had higher specificity (0.92 vs 0.80, p<0.001) and positive predictive value (24% vs 11%, p<0.001) for identifying cases at risk for metastasis/death, and C statistic was superior for BWH (p<0.001). BWH T2 ten-year cumulative incidence of metastasis/death was 37% (21-60%).Two-center cohort CONCLUSIONS: and Relevance: BWH and AJCC BCC staging both capture all metastases and deaths in upper stages. However, BWH does so in half the number of cases thus minimizing inappropriate up-staging. Risk of metastasis or death in BWH T2 BCC is sufficient to warrant surveillance for recurrence and clinical trials of adjuvant therapy.