A 50-year-old man with ankylosing spondylitis who developed neutropenia after treatment of etanercept, with two positive rechallenges, and after the first infliximab infusion, is described. Although leukopenia and neutropenia related to etanercept and infliximab have been described as rare adverse events from clinical trials data, their mechanism of action are unknown. This patient developed recurrent mild neutropenia after exposition of two different antitumor necrosis factors; therefore, it seems to be an adverse reaction related to the therapeutic group. Doctors should be aware of this potentially severe adverse effect in patients treated with antitumor necrosis factor.