Immune thrombocytopenic purpura (ITP) is an acquired disorder characterized by thrombocytopenia, increased platelet destruction, and the inhibition of platelet production by specific autoantibodies. Previous studies have reported improvements in ITP following the eradication of Helicobacter pylori (H. pylori) infection. We, herein, investigated the relationship between initial therapy for ITP and lymphocyte counts at diagnosis. We retrospectively examined 52 adult patients with ITP between March 1998 and March 2013. Standard H. pylori eradication therapy was performed in 31 patients, and lymphocyte counts were compared before and after this therapy. At the diagnosis of ITP, lymphocyte counts in H. pylori-infected patients were significantly higher than those in H. pylori-negative patients (1.92 ± 0.68 × 10(9)/L vs. 1.42 ± 0.67 × 10(9)/L; p = 0.010). H. pylori eradication was successful in 6/11 patients (54.5 %) and the platelet count increased in 4/11 H. pylori-positive patients (36.4 %) who received eradication therapy. On the other hand, eradication therapy was also administered to 15 patients without H. pylori infection, and responses were obtained in some H. pylori-negative patients receiving eradication therapy (9/15). Furthermore, lymphocyte counts were significantly higher in patients who achieved a complete response receiving H. pylori eradication therapy than in patients who did not achieve a complete response (2.4 ± 0.59 × 10(9)/L vs. 1.37 ± 0.60 × 10(9)/L, p = 0.0023). The response of ITP patients to the initial treatment may be predicted by measuring the lymphocyte count at diagnosis. Further studies that analyze lymphocyte subsets and the cytokine network are needed to elucidate the underlying mechanisms.