Forty-four squamous cell carcinomas (SCC) of the skin and lip were observed in 9 of 464 renal homograft recipients. Clinically and histologically the SCC's fell into two groups. Two patients with widespread warts, suggestive of epidermodysplasia verruciformis, showed multiple SCC's predominantly on the upper extremities which were associated with minimal solar elastosis of the adjacent dermis. The other seven patients did not have widespread warts; their SCC's occurred predominantly on the head and neck and were associated with prominent solar elastosis of the adjacent dermis. The degree of solar elastosis was particularly striking in view of the young age of this group (mean age: 37 years). Inflammatory cellular response to the transplant SCC's was significantly diminished in comparison with a group of control SCC's from non-immunosuppressed patients. In both transplant groups sunlight appears to be an important etiologic factor; in the first group viruses may also be important.