Erythroderma is a medical condition characterized by inflammation involving skin over 90% of the body’s surface area. This condition can result in high mortality rate and many systemic complications including fluid and electrolyte imbalance, infections, thermoregulatory disturbance and high output cardiac failure. In Thailand, limited data have been reported in the literature. This study aims to investigate epidemiologic, clinical and histologic data relevant to etiologies of erythroderma among adults. We performed a retrospective study among all patients acquiring erythroderma, aged above 16 years and visiting at the Division of Dermatology, Department of Internal Medicine, Phramongkutklao Hospital, Thailand from January 2015 to December 2019. The following data were recorded: personal data, medical history, clinical manifestations, histopathologic results, possible etiologies, laboratory profiles, treatment methods and outcomes. During the 5-year study, 35 patients with erythroderma were collected. Men outnumbered women 6:1 (30 men and 5 women). The age of these patients ranged from 18-90 with mean age of 66.4 years. Idiopathic was the predominant etiology with 20/35 cases (57.1%), followed by drug eruption (17.1%). Herbal medicine (33.3%) and spironolactone (33.3%) were the most implicated drugs. Pre-existing skin diseases were observed including psoriasis (17.1%), pityriasis rubra pilaris (2.8%) and malignancy associated erythroderma (2.8%). Epidermal spongiosis was the most common histological feature observed in all etiologies (85.7%), (p=0.029). Complete clearance was obtained in 15/35 (42.8%). Death 2/35 (5.6%) occurred in one patient with drug reaction and one patient with pemphigus vulgaris associated erythroderma complicated with sepsis. Although data are limited, erythroderma remains a serious condition effecting quality of life of patients. Our study demonstrated further epidemiology, etiologies and clinicopathologic information of erythroderma among Thai patients.