Thrombocytopenia is a group of heterogeneous disorders of varying etiology and involving deficiency of platelets. Platelet volume parameters are significant especially in the diagnosis of causes of thrombocytopenia. The platelet volume parameters have been widely available as part of full blood count profile on automated hematology analyzers. To evaluate the relationship between platelet volume parameters and causative process in thrombocytopenia Methods: PLCR of 500 cases of thrombocytopenia (TCP) and 300 control cases having normal platelet counts were recorded. The analysis was done by Sysmex KX 21 cell counter and every case was reassessed by Peripheral Smear (P.S.) examination and if necessary also by the manual method. Only those cases that had sufficient clinico-hematological work up were included in the study. Results: Cases were grouped according to the most predominant mechanism of Group A-Accelerated platelet destruction, Group B-Impaired platelet production, and Group C-Abnormal platelet pooling. The age range was from 1 day to 90 years. The commonest age group for thrombocytopenia was between 21-30 years accounting for 88(18%) cases. 75(15%) cases belonged to both 31-40 and 41-50 age groups. The mean platelet large cell ratio P-LCR % was 22.64 ± 7.13 and in Group A it was 31.68 ± 8.36 and in Group B was 19.50 ± 5.51 and Group C was 31.48 ± 9.09. The Z test was performed between A, B and C Group with the control group of all the parameters of the platelet count. The P-LCR of accelerated destruction Group A, B, C and Vs Control were all significant values <0.05. Conclusion: Platelet Large cell ratio and the Platelet distribution width showed a direct linear relationship in all groups of Thrombocytopenia as well as the control group. Decreased production of platelets in cases of thrombocytopenia can be differentiated from other two groups of thrombocytopenia with the help of all the three parameters MPV, PDW and P-LCR as the differences are statistically significant.