Based on electron microscopic features, recessive congenital ichthyoses have recently been divided into four subgroups designated ichthyosis congenita (IC) types I, II, III and IV, Type II is characterized by cholesterol clefts in the horny cells, type III by perinuclear elongated membranes in the granular and horny cells, and type IV by masses of lipid membranes in granular and horny cells. Clear electron microscopic criteria for type I are lacking, although the presence of lipid droplets in the horny cells has been suggested as a criterion. In the present study we included ichthyosis patients with (i) recessive inheritance, (ii) erythrodermic fine scaling, (iii) lack of line structural markers of IC types II‐IV, Patients with ichthyotic syndromes were excluded. The case material consisted of 21 patients from 14 families. Eight were collodion babies at birth, but three were normal. Nine had ectropion, the flexures were affected in 12, and the palms and soles were thickened in all but one patient. On electron microscopy lipid vacuoles in the horny cells were common, but were absent in four patients. Changes in other lipid‐related structures, including keratinosomes, were common. We conclude that currently type I can be diagnosed only by excluding the other types of ichthyosis. Clinically, IC type I corresponds to classical non‐bullous congenital ichthyosiform erythroderma, but there is marked heterogeneity among affected individuals.