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In a review of all cases of porokeratosis histologically diagnosed in our Department during the period 1991-98 we found that 12 patients (22%) were in their seventh to ninth decade. In all 12 (2 males and 10 females) the age of onset of the disease varied between 58 and 89 years (mean age 68.6 years). The clinical picture was similar in all the patients, with the number of lesions varying from a few to 20-50 annular plaques 10-15 mm in diameter, localized mainly on the lower limbs. We suggest that our patients had a very mild form of disseminated superficial actinic porokeratosis confined to the extremities with an unusually late onset. This peculiar variety of late-onset disseminated superficial actinic porokeratosis may represent a type of immunosuppression-induced porokeratosis where the pathologic clone for porokeratosis is present but remains latent until the amount of sun exposure, together with the physiological age-related lowering of immunocompetence, bring about its proliferation. [ABSTRACT FROM AUTHOR]