To identify nonmelanoma skin cancer patients with squamous cell carcinoma (SCC) who are at greatest risk of disease-specific mortality. Prospectively enrolled patients with a minimum of one pathologically confirmed skin SCC lesion, definitive treatment of the SCC lesion(s) resulting in no evidence of disease, and at least 2 months of follow-up after definitive treatment were eligible for the present longitudinal analysis. They received comprehensive clinical, pathologic evaluations and follow-up for patterns of failure and mortality. We enrolled 210 patients (187 men and 23 women) with a total of 277 skin SCC lesions and a median enrollment age of 68 years (range, 34 to 95 years). Median follow-up of surviving patients was 22 months. Three-year overall and disease-specific survival (DSS) rates were 70% and 85%, respectively. In univariate analyses, the clinical-pathologic factors associated with adverse DSS were local recurrence at presentation (P = .05), invasion beyond subcutaneous tissues (P = .009), perineural invasion (P = .002), lesion size (P = .0003), and depth of invasion (P = .05). Statistical models identified a homogeneous high-risk group of patients with lesions > or = 4 cm, perineural invasion, and deep invasion beyond subcutaneous structures. Three-year DSS was 100% for patients with no risk factors versus 70% for patients with at least one risk factor. Lesion size > or = 4 cm and histologic evidence of perineural invasion and deep invasion beyond subcutaneous structures were the clinical-pathologic factors most significantly associated with disease-specific mortality in skin SCC.