We reviewed 82 cases of erythroderma, including clinical, laboratory, and biopsy material. The diseases most commonly associated with erythroderma were drug eruptions (34%), preexisting dermatoses (30%), and lymphoreticular neoplasms (20%), especially cutaneous T cell lymphomas (CTCL). The prognosis was related to the associated process; all deaths occurred in the drug or lymphoma groups. The clinical presentation of erythroderma was fairly uniform, with malaise (34%), pruritus (36%), and a subjective chilly sensation (34%) the most common symptoms. Keratoderma of the palms and soles (37%), mild generalized adenopathy (26%), and hepatomegaly (9%) were also common. Splenomegaly was rare (1%). Skin biopsy revealed the cause in 43% of the patients, but lymph node biopsy was not generally helpful in the initial evaluation. Although numerous laboratory values were abnormal, most findings were nondiagnostic and were related to the inflammatory process. A major exception was the Sezary cell preparation, which was selective for CTCL. A previously undiagnosed chronic erythroderma in a patient with no underlying skin disease may be the initial manifestation of CTCL. Thus, repeated evaluations and close follow-up are recommended.