Background <p>We have already reported that anti-insulin antibodies are produced at a fairly high frequency in type 2 diabetic patients treated with insulin analogues, and the amount of insulin requirement was significantly higher in antibodies carriers than in non-carriers. On the other hand, insulin autoantibody production by clopidogrel, which has an antiplatelet effect, has been reported. Therefore, we investigated the effect of concomitant use of antiplatelet agents on anti-insulin antibodies production in type 2 diabetic patients treated with insulin analogues.</p> Methods <p>Anti-insulin antibodies were measured in 150 type 2 diabetic patients using insulin analogue and 15 patients without insulin treatment but with antiplatelet agents. Among insulin treated patients, 62 had concomitant use of antiplatelet agents.</p> Results <p>The overall positivity of anti-insulin antibodies in the insulin-treated patients was 25.3%. On the other hand, the positivity rate in those not on antiplatelet agents (<i>N</i> = 88) was 15.9%, whereas the rate was significantly (<i>P</i> = 0.002) higher in those on antiplatelet agents (<i>N</i> = 62), at 28.7%. No one has anti-insulin antibodies in patients without insulin treatment. The antibodies-positive rate was also significantly higher than that of non-users of antiplatelet agents, irrespective of the type of antiplatelet agent. The amount of daily insulin requirement had a significant and positive association with antibodies positivity by stratified and multiple regression analyses.</p> Conclusion <p>These results strongly suggest that antiplatelet agents affect the increased production rate of anti-insulin antibodies by insulin analogues and may have contributed to increased insulin dose requirement via positivity of anti-insulin antibodies.</p>