Cutaneous squamous cell carcinomas (SCC) arising in actinically damaged skin, unassociated with chronic inflammation or injury, are generally regarded as nonaggressive lesions. These tumors occasionally recur or metastasize, however, as do de novo SCC. The authors reviewed 63 patients with cutaneous SCC of the trunk or extremities, excluding lesions that developed in known high risk settings, in order to explore the potential of histologic microstaging as a prognostic indicator. Fiftyfour patients (86%) were free of recurrence following primary surgical therapy. Nine patients (14%) had either local recurrence or metastases; five of these (8% of the entire series) died of their tumors. Tumor behavior correlated best with the level of dermal invasion and the vertical tumor thickness. All tumors that recurred were 4 mm or more thick and involved the deep half of the dermis or deeper structures. All tumors that proved fatal were at least 10 mm in maximum thickness, and the four lethal lesions that could be evaluated for level of invasion extended into subcutaneous tissue or deeper structures. The thickness and level of invasion of cutaneous SCC appear to represent important prognostic factors and may be relevant indicators for wide field resection and/or elective lymph node dissection.