A retrospective study was performed to elucidate the characteristics of heparin-induced thrombocytopenia (HIT) in newly treated hemodialysis (HD) patients who essentially required anticoagulation with unfractionated heparin (UFH). Seventy-eight patients suspected of having HIT within 3 months of starting HD with UFH were selected for this study. Their platelet counts were routinely followed, and anti-PF4/heparin complex antibodies (HIT antibodies) were measured with enzyme-linked immunosorbent assay (ELISA) until the titer became negative. The characteristics of thrombocytopenia were a platelet count of ≤150 × 109/L and/or decrease of ≥30% and as caused by the intermittent use (3 times/a week) of UFH during HD. Fifty-five patients showed unexpected clotting in the extracorporeal circuit and/or arteriovenous fistula (AVF) thrombosis, while 23 patients had neither of these complications. The patients were classified into HD-related and non-HD-related thrombus groups. The impact of various combinations of the 3 clinical factors (thrombocytopenia, timing, and HD-related thrombus) and the results of ELISA as a laboratory factor were examined. A combination of 2 platelet factors (thrombocytopenia and timing) and ELISA positivity did not reveal the presence of HIT, while a combination of the 3 clinical factors and a positive ELISA improved the accuracy of HIT diagnosis. The findings on the 4-factor combination were supported by high rates of seroconversion in a serotonin release assay. Combining appropriate clinical factors and a positive ELISA may lead to the proper management of HD patients suspected of having HIT. In conclusion, while HD patients showed a drop of ≤150 × 109/L or ≥30% on days 7 to 30, unexpected clotting in the circuit and/or AVF thrombosis was considered as a sign of HIT development.