Autosomal recessive exfoliative ichthyosis (AREI) results from mutations in CSTA, encoding cysteine protease inhibitor A (cystatin A). We present a 25-year-old man from Iran with consanguineous parents, who presented with congenital erythroderma, hyperhidrosis and diffuse hyperkeratosis with coarse palmoplantar peeling of the skin, aggravated by exposure to water and by occlusion. Candidate gene analysis revealed a previously unknown homozygous loss-of-function mutation c.172C>T (p.Arg58Ter) in CSTA, and immunostaining showed absence of epidermal cystatin A, confirming the diagnosis of AREI. Ultrastructural analysis by transmission electron microscopy showed normal degradation of corneodesmosomes, mild intercellular oedema in the spinous layer but not in the basal layer, normal-appearing desmosomes, and prominent keratin filaments within basal keratinocytes. Thickness of cornified envelopes was reduced, lamellar lipid bilayers were disturbed, lamellar body secretion occurred prematurely and processing of secreted lamellar body contents was delayed. These barrier abnormalities were reminiscent of (albeit less severe than in) Netherton syndrome, which results from a deficiency of the serine protease inhibitor LEKTI. This work describes ultrastructural findings with evidence of epidermal barrier abnormalities in AREI. What's already known about this topic? Recently, loss-of-function mutations in CSTA, encoding cysteine protease inhibitor A, were reported to cause autosomal recessive exfoliative ichthyosis (AREI). There is evidence for a key role of cysteine protease inhibitor A in desmosome-mediated cell-cell adhesion within the basal and spinous layers of the human epidermis. What does this study add? We report a novel homozygous loss-of-function mutation in CSTA. Transmission electron microscopy revealed epidermal barrier abnormalities in AREI. We compare the morphological characteristics between AREI and Netherton syndrome (also caused by a protease inhibitor deficiency).