Two collodion baby girls with disorder evolving into lamellar ichthyosis were followed by light and electron microscopy. Light microscopically, the neonatal collodion skin was characterized by a thick compact stratum corneum which was PAS positive in its upper two thirds, by a thin stratum granulosum and by a non‐acanthotic stratum spinosum with normal mitotic activity. Electron microscopically, the upper stratum corneum appeared pathological, whereas the lower part was normal except for some minor parakeratosis. The main alterations in the underlying stratum granulosum were diminished tonofibrils and keratohyalin. Biopsy specimens taken at the age of 2 weeks were typical for lamellar ichthyosis and showed hyperkeratosis with focal parakeratosis, a thickened stratum granulosum in which the cellular content of keratohyalin and tonofibrils was moderately diminished, and acanthosis with increased mitotic activity. It appears that the ultrastructural changes of the stratum granulosum, seen in lamellar ichthyosis, are already present in the collodion skin of the newborn, at a time when the epidermis does not yet show an increase in mitotic activity.