Background: The effects of body mass index (BMI) and blood groups on immune thrombocytopenia (ITP) are not clearly known. This study aims to investigate the effect of BMI and blood groups on the treatment of ITP. Materials and Methods: All cases included in this study were primary ITP patients. Body measurements, treatment history, demographic, and laboratory data were recorded. The data obtained were analyzed after the patients were divided into groups based on BMI and blood groups. Results: The study included 68 (100%) cases, 53 of which were female (77.9%). The median age of the cases was 44 years (min: 18, max: 87). The median BMI was 28.05 (min: 17.6, max: 51.4), and patients with normal weight, overweight, and obesity were found in 24 (35.3%), 20 (29.4%), and 24 (35.3%) cases, respectively. According to blood groups, 29 (42.6%), 20 (29.4%), 11 (16.2%), and 8 (11.8%) cases had blood groups A, O, B, and AB, respectively. The analysis of BMI and blood groups together with demographic and laboratory variables revealed that patients with obesity had a higher mean age (p=0.049) and lactate dehydrogenase levels (p<0.001) than other BMI groups. In the analysis of treatment responses, it was found that using eltrombopag in the second-line treatment in the patients with normal weight group was associated with a better response than other BMI groups (p=0.025). Conclusions: This is the first study to look investigate the relationship between BMI and ITP therapy. According to the results of our study, we believe that BMI should be considered in the selection of second-line therapy for ITP. [ABSTRACT FROM AUTHOR]