Some 30-50% of cases of atopic dermatitis (AD) are believed to be associated with autosomal dominant ichthyosis vulgaris (ADI). The diagnosis of ADI can be proved by the ultrastructural demonstration of fewer and abnormal keratohyalin (KH) granules in all ADI patients, even in clinically unaffected skin. To prove the suggested frequent association of ADI with AD, an ultrastructural investigation of dry skin of 49 AD patients was performed. Only in 2 (4%) patients ADI could be confirmed by electron microscopy. In 17 patients, including the 2 patients with abnormal KH, hyperlinear palms were clinically seen. The present study yields evidence that hyperlinear palms, if present, and dry skin are in most cases a phenotypic marker of AD and not a sign of concomitant ADI. A histologically absent stratum granulosum in AD does not signify by itself a manifestation of concomitant ADI.