A 48-year-old lead worker was found to have a cystic renal carcinoma during an evaluation of his occupational lead poisoning. Clinical studies showed elevated blood lead levels, impaired urinary concentrating ability, and reduced creatinine clearance. Histologic and electron microscopic studies showed this cystic tumor to be similar to renal carcinomas observed in animals with prolonged lead exposure. Lead content of the tumor was elevated (2.49 μg/gm) in comparison with adjacent renal tissue and with normal adult levels. In light of previous animal studies, this case adds increased evidence to the concern over the carcinogenic potential of prolonged lead exposure.