Erythroderma, or exfoliative dermatitis, is an inflammatory disorder characterized by erythema and scaling, affecting most of the skin surface. It may be a result of many different causes such as previous dermatoses (psoriasis, eczema, atopic dermatitis [AD], pityriasis rubra pilaris, and pemphigus foliaceous), drug reactions, malignancies (mycosis fungoides [MF], Sezary syndrome, adult T cell leukemia/lymphoma), infections, and idiopathic disorders. Regardless of the etiology, the clinical appearance of erythroderma is similar in all patients. The most prominent physical examination findings in almost all patients are diffuse erythema and scaling. In a 2-year period, 47 patients who were hospitalized and treated in our department were included in the study. We classified patients into seven subgroups: psoriasis, AD, drug-induced erythroderma, MF, pityriasis rubra pilaris, bullous pemphigoid, and polymorphous light eruption. All patients had a biopsy during the acute stage and diagnoses were histopathologically confirmed. Some patients had multiple biopsies for histopathological confirmation. In our study, the majority of the patients were men over the age of 54. The most common etiological cause of erythroderma is psoriasis. We aim to analyze clinical, laboratory, and histopathological findings of erythrodermic inpatients prospectively in Istanbul University-Cerrahpasa Cerrahpasa Medical Faculty between January 2018 and 2020.