ABSTRACT
To study the causes of thrombocytosis in Medical City Hospital, 151 patients with such a problem were included, The were randomly taken from teaching laboratory records [any patient with platelets count of more than 450 x 109/L for the period from 1st of December to the 30th April 1992. All patients were followed in different wards and out-patient departments and were fully studied clinically with investigations to reach a final definite diagnosis. They were 77 females and 76 males with platelet count ranging from "457 x 109 / L with an average of 676 x 109/L. The cause according to their incidence were as follows: malignancies, acute infections, myeloproliferative disorders, post surgical, post splenectomy, iron deficiency anemia and miscellaneous cause. It was concluded from the study that causes of thrombocytosis at the Medical City Hospitals are not very much different from what was previously reported