In a case control study of the prevalence of palmar keratoses in 69 bladder cancer patients, 66 lung cancer patients, and 218 hospital controls palmar keratoses were more common in the cases, especially among those with cancer of the bladder. Above the age of 50 years, 87% of bladder cancer patients and 71% of lung cancer patients but only 36% of the controls had one or more keratoses. The prevalence increased with age and keratoses were more common in males. No features could be found which distinguished the keratoses in cases from those in controls.