Although hairy cell leukaemia was first described 40 years ago, it is only in the last decade that newer therapeutic agents have enabled effective treatment. The purine nucleoside analogue, 2-chlorodeoxyadenosine (2-CdA) is currently considered as first-line therapy with a very high rate of complete remission. Although adverse events with 2-CdA are increasingly recognized, severe cutaneous reactions have been reported rarely. We describe two consecutive patients treated with 2-CdA for hairy cell leukaemia who both suffered extremely severe cutaneous reactions, one of which was life-threatening.