A case of a 17-year-old Japanese-Canadian boy with a 2-year history of skin lesions relevant to confluent and reticulated pa-pillomatosis (CRP) is reported with electron microscopic findings. He had scattered skin lesions of brownish-colored, rough-surfaced, fine-scaled patches and plaques distributed on the nape, shoulders, and both flanks, extending to the chest and back. Importantly, they showed reticular or confluent arrangement. There was no family history of the same skin lesions. The histology showed epidermal papillomatosis and mild acanthosis with a marked hyperkeratosis. Electron microscopically, the skin lesions consisted of the following abnormal findings: (1) a marked alteration of cornified cell structures showing snake coil-like, or triangle-like stacks, (2) a marked increase in the number of lamellar granules in the granular layer, (3). an increased number of melanosomes in the horny layers, and (4) no significant fine structural changes of epidermal melanocytes. This is the first electron microscopic report on CRP suggesting that the pathophysiology of this disease is related to abnormal keratinocyte differentiation.