A 56-year-old woman with mycosis fungoides developed acrocyanosis each time treatment with interferon alpha(2a) was started. Acrocyanosis disappeared after discontinuing therapy. Immunological study performed while acrocyanosis was present showed elevated antinuclear antibody (ANA) titers and circulating immune-complex levels. Long-term interferon treatment has been related to autoimmune side effects. Raynaud's phenomenon has been observed in patients undergoing interferon treatment associated with elevated ANA titers, to cryoglobulinemia or to arterial occlusion. Acrocyanosis has never before been described as side effect in patients undergoing this treatment. We believe that our patient's acrocyanosis must be considered a side effect of interferon.