Erythroderma is a scaling erythematous dermatitis involving 90% or more of the cutaneous surface. Psoriasis and eczema are the most common dermatoses underlying erythroderma. Cutaneous T cell lymphomas can also cause erythroderma. Differential diagnosis between psoriatic erythroderma and lymphomatous erythroderma is often challenging. Tumour necrosis factor-alpha inhibitors are a new class of drugs used in the treatment of psoriasis, even in erythrodermic psoriasis. The effects of anti-tumour necrosis factor-alpha in cutaneous T cell lymphomas have not yet been established. Consequently, it is mandatory to treat an erythrodermic psoriatic patient with tumour necrosis factor-alpha blockers only if a lymphoproliferative cutaneous disorder has been excluded.