Rarely, tumour necrosis factor (TNF)alpha antagonist therapy has been associated with de novo psoriasiform eruptions. This is unusual in that these same drugs are used to treat psoriasis. Most of these cases involve the palms and soles, yet palmoplantar pustular psoriasis represents only 1.7% of all cases of psoriasis. Keratoderma blenorrhagicum is a psoriasiform rash that occurs primarily on the palms and soles of some patients with reactive arthritis. It is grossly and histologically indistinguishable from pustular psoriasis. Chlamydia trachomatis is a common aetiological agent for reactive arthritis, and in vitro studies have shown that chlamydial replication is inversely proportional to TNFalpha levels. Three patients taking TNFalpha antagonists are presented who developed such lesions and who were found to be positive for C trachomatis DNA in the affected skin. It is proposed that these psoriasiform lesions may not be psoriasis, but rather keratoderma blenorrhagicum.