Proliferating cell nuclear antigen (PCNA) is a nuclear protein which is correlated with the S-phase of the cell cycle and has been utilized by many investigators as a marker of cell proliferation. A previous immunohistochemical study revealed increased PCNA staining in clinically and histologically aggressive basal cell carcinoma and the present study evaluated the prognostic value of PCNA in clinical recurrence of primary basal cell carcinoma. Thirty patients with primary basal cell carcinoma (BCC) treated with shave biopsy followed by electrodesiccation in 1989 and have been regularly followed up for local recurrence were selected for this study. The histology of their primary BCC's was reviewed and the presence of PCNA in the tumor cells was studied immunohistochemically. Ninety-six percent of the non-recurrent BCC's had < 10% of tumor cells showing a positive staining for PCNA whereas 100% of the BCC's that recurred showed more than 30% of tumor cells staining positive for PCNA. In comparison, 88.9% of the non-recurring group showed non-aggressive histological features and only 66.7% of the recurring group was aggressive by microscopic appearance. In summary, the PCNA staining appeared to be superior to traditional histologic features in predicting clinical recurrence in primary BCC's and further prospective studies in a larger patient group are warranted.